What Rocko said about the crap between the cylinders is so true. I actually pulled my old 283 to put it on a stand in the driveway, then I pulled the freeze plugs and flushed the block thru the holes with one of these
https://www.homedepot.com/p/Gilmour-...E&gclsrc=aw.ds I turned it upside down and did it some more and I made a huge rusty powdery puddle of nastiness. Gunk just came rolling out of those freeze plug openings. It all went well. I drained the oil first course, pulled the carb and distributor and sealed those holes with plastic bags and flashing tape and just blasted the water jacket until the water finally ran clean.