Best starting point for V8 swap

I would get a 85 to 87 318 from a car. Most truck/van engines have seen a hard life.
Many of their parts wont work in a car. Even the radiater from a Gran Fury or Fifth Ave will go in the A-body with a little effort. The right leanburn 318 might not need more than block flush, timing set, valve stem oil seals, and a oil pump, to run another 100 K miles.
Replace the leanburn with common electronic ignition and happy moparing.