it's best to get it ALL apart, cleaned and then take it to the engine shop to be measured. most of these guys spend a good amount of coin in their precision measuring tools and appreciate it when the engine comes to them fairly grease free.
if you haven't had an engine apart in a while, or never, you should start with a car wash trip to get rid of most of the larger deposits. I say this because if you don't know the engine then you maybe don't know where all the bolts are and they can be hidden under a layer of goo. next, find a spot where you can work and spread stuff out. have a few boxes ready for parts and a felt pen to mark the boxes. some gallon paint cans with small holes punched in the bottom work well for parts catchers and when you get it to the engine shop they will love you because they simply get put in the "hot tank" as is so no problems with getting the parts mixed up while in the tank with other peoples parts, plus, when they come out of the tank the parts are easily hosed off while inside the paint can so nothing gets lost. this is assuming you have already drained the engine oil. next block the engine up so it can't fall over on you (these things are heavy) and start by removing the bell housing, clutch etc from the rear (clutch has to come off first, then flywheel so you can access the bell housing to engine bolts). if you have an engine stand then now would be the time to get it mounted up. remember that this is a tall engine and a heavy one too so make sure to use the rotation stop pin so it doesn't spin on you while you're working on it.
next, remove the pulley assembly from the front (you may need a puller AND the crankshaft protector part that keeps the puller bolt from damaging the crankshaft) and any accessories like generator and bracket, water pump, distributor, coil, carb, fuel pump, oil filter can (if used), intake and exhaust manifolds, any sensors left in the engine, oil dipstick tube, engine draft tube, thermostat and housing, spark plugs etc. now you should be down to the bare bones. it's time to remove the tin work starting with the valve cover and lifter cover. you can also remove the timing cover as well. next it's time to take the rocker shaft assembly off. it is a good idea to keep mated parts together here so keep track of what pushrod went where and also which end is facing up. what I have done in the past is use a box large enough to keep all the pushrods in and deep enough so you can close the box, push a rod through the cardboard top and the rod will be kept resonably safe from damage or getting mixed up. all the rods go in as oriented from the engine, so the bottom of the rod is pushed through the lid and the top of the rod is sticking out. make a mark on the box, physically, so if the box gets grease or oil impregnated you still know which end of the box is front. the same goes for the lifter because they need to go back on the same cam lobe they wore in on. again, a box with some cut outs or a 2x4 with some holes drilled (not all the way through) works good to keep things in order. for the rocker shaft, you will also need to keep the rockers oriented in the same position on the shaft. when you dissassemble the shaft you can use a piece of wire to keep all the parts on. keep them in order and mark the front by placing something, like a washer or nut, on the wire next to the very front rocker on the wire. once you have all the valve train dissassembled and stowed it is time to remove the head. start by loosening the head bolts in the center of the head and working in a circular pattern towards the outside. these heads are quite long so it is best to do it this way to eliminate as much possible distortion as you can. have a couple of pieces of wood ready to lay the head down on when you take it off, this will reduce the possibility of scratching the head gasket surface. sometimes the head gasket can be stuck pretty good and you may need to use a prybar in a head bolt hole to get the head loose, just be carefull not to get over ambitious and end up with the head sitting on your toes. once the head is off you can also remove the gasket and check each piston to see if there is still a mark on it to denote forward facing. now is a great time to ridge ream the wear mark from the top of each cylinder. you will need a special tool for this but some parts stores will rent or loan them out and if not the tool is fairly cheap anyway. the ridge at the top of each cylinder needs to be removed so that when the pistons are pushed out past the ridge the piston rings won't get caught up on the ridge and break a piston in the "ring land" area (the small spaces of piston that is between the ring grooves). once that is all done, then roll the engine over for access to the oil pan etc. if working on the floor a piece of plywood works well as a base for the engine to sit on to protect the head gasket surface from getting scratched up. next is to remove the oil pan, then the oil pump pick up tubing and the oil pump. the pump may end up being a leaker once it is unbolted because it is still full of oil so a 5 gallon bucket is nice to place it and the pick up tube into, cleaner shop floor that way. next you will need to look at the bearing caps on all the main and rod bearings to see if they are marked. each rod cap should have a number stamped into it to designate which cylinder it came from and each rod should also have a number punched into it right next to that. it is so the rod and cap stay oriented the same way. the main bearing caps also need to be marked from front to rear and also some sort of designation to say which way faces forward. now you will need a couple of short pieces of rubber hose that will fit fairly tightly over the rod bolts and be a little bit longer than the bolts. this is so that when the nuts are undone and the bearing cap is removed the rubber hose can be placed over each rod bolt and that will eliminate the chance of the rod bolt bumping the crankshaft and leaving a mark on the journal as it goes past when the piston is pushed out of the cylinder. once everything is marked correctly you can start by undoing a rod. I usually start at the front and work back just for simplicity sake but it doesn't really matter. rotate the engine so the rod for your cylinder is as far out of the engine as possible. this makes it easy to work an and also leaves less chance of marking the crankshaft while pushing out the piston later. undo the rod cap nuts, remove the cap and bearing shell, then place the rubber hoses over each rod bolt that is sticking out of the rod. use a length of wooden broom stick handle, or similar, to push the piston out the top of the engine or, if the engine is sitting on the head surface, push the piston as far down as possible. leave the rubber hoses on the bolts until the piston is out of the hole and the bearing cap can be placed back on the rod again. this will lessen the possibility of marking a cylinder bore with the rod bolt as it bounces around in there. next the crankshaft can be rotated to the next cylinder and the procedure copied until all the rods are undone and the pistons pushed down towards the head end the cylinders. when done this and all the pistons have been removed and rod caps placed back on, the next step is to remove the camshaft. it needs to be rotated to show 2 screws, through the 2 holes in the cam gear, that hold the cam thrust plate to the engine. remove the screws, place them somewhere so you won't lose them, then the cam should pull straight out the front of the engine but will require support as it comes out. you may want to check the timing marks before doing this so you understand how they line up for when the assembly part comes. behind the camshaft gear is a flat plate that is held on with a couple of flat head (usually) bolts. you may need an impact driver to get the bolts out but once the plate is removed it will leave access to the crankshaft for easy removal. once the plate is removed you can remove the main bearing caps using the same method as the cylinder head bolts, start in the middle and work your way out to avoid any stressing/warpage of the block. when the main caps are all removed the crankshaft can be lifted straight out of the block. after this is complete you can go around the block and remove the frost plugs, oil gallery plugs etc so when it is cleaned the wash tech will be able to get any crud out of all the passageways. just be aware that.
this is all "off the cuff" since I haven't had a 235 apart for many years. here is a couple of links to sites that have some good info.
http://devestechnet.com/Home/Project1959235
http://chev235guy.blogspot.com/2015/...evolution.html
this is one from lowrider magazine, it is the assembly section so there is probably a dissassembly section as well. maybe worth some digging around if it interests you.
https://www.lowrider.com/how-to-tech...ild-235_engine