[dsraven]

The 92 vortex should have a one piece rear main seal that is held in by a bolt on bracket affair. This bracket also is the sealing surface for the oil pan gasket. If yours is a newer engine and isn't leaking then maybe leave well enough alone.
If unsure about whether the trans torque converter seal was done at the same time as the newer engine then you could pull the trans off and check that seal. Once the torque converter is pulled off the torque seal is easy to change. You can push a new seal in with a length of ABS plumbing pipe or some clean exhaust pipe. There will likely be some teflon style seals on the input shaft too. Those can be a little tricky to change and not tear or distort when you slip the converter back on so you decide on whether you change the converter seal or not. I also suggest to pull the trans pan and change the filter and gasket while it's out of the vehicle. You get to see what's in the pan that way. Lots of times I will install a drain plug in the pan while it's off just because. The dipstick and tube can be easily pulled out and a plug installed in the rubber grommet in the trans. Sometimes a wooden broom handle is the right size. It just makes it easier to work with if the tube is out of the way. Same goes for the trans cooler lines. They are just flare fittings probably so plugs are easily sourced to cap the trans fittings. Then the cooler lines dont get bent outta shape while working on other things and moving stuff. Plus the lines can be properly flushed/cleaned out and capped until you need then. I have used those foam style earplugs to blow through the lines using compressed air after flushing the lines out. Then cap lines with vacuum plugs on both ends till ready to install

To pull the trans off, remove starter and converter splash shield etc, then undo the converter to flexplate(flywheel) bolts and the push the converter back into the trans. Then undo the bell housing bolts to split the trans and engine. I usually use a chunk of 2x4 against the converter and use some wire through the bell housing bolts to keep the converter from slipping out or falling out. The converter is notched and fits into the oil pump in the trans so if it slips out on you be sure to carefully install it so as not to tear those teflon input shaft seals, and also turn the converter as it goes in to ensure the converter notches have fit into the pump drive correctly and the converter is fully seated. Failure to do that will mean the engine and trans wont quite come together all the way when assembling. This has resulted in a lot of broken bellhousings or transmission front pumps due to guys using the bellhousing bolts to pull the 2 parts together when this happens. Screw the bolts or nuts back on the converter after disassembling so they dont get lost and to protect the threads. On assembly Check the flex plate for cracks around the bolt holes and if you take the flex plate off be sure to install the correct way around. Pics before taking stuff apart is a good idea. Using a paint marker to mark parts can also help you remember orientation.
If you are unsure of the status/quality of the engine rebuild now would be a good time to check a few things. Pulling the pan off and plastigaging a couple of con rod bearings would be a good indicator. Plus it gives you a look inside. Or, clean it all up and install it as is. It isn't that tough to pull an engine out of one of these old trucks especially if you take the front body clip off.
Good idea to keep a bunch of parts off the donor, like manifolds and driveshaft etc. I usually try to keep the whole donor until the project vehicle is running if I have room. Better than making trips to the store or wrecker for parts you just sent for scrap.
These trucks came with small block Chevy engines but the engine mounts were bolted on the front instead of the sides and the trans hung off the bellhousing instead of having a trans crossmember. The bellhousing had it's own mounts on a crossmember behind the engine which also served purpose of keeping the frame from flexing in the area of the front cab mounts. If that crossmember is removed to incorporate the newer style of driveline just keep an eye on the cab mounts and door/fender/hood gaps and fitment as the truck gets used after the engine transplant. Issues with the body fitment can mean the frame is flexing and needs some extra support in that area where the old crossmember was.
Sorry for the rant, I got on a roll, haha.
Post up some pics as you work through it.