Chevrolet Repair: rear main seal, monte carlo ss, aero coupe

Question
I have a 87 Monte Carlo SS Aero coupe with the 305. The bottom end is fried so i am looking into buying a new engine.  My biggest concern is about the 1 or 2 piece rear main seal.  If i wanted to buy an engine out of an older car a 350 or 383 with a 2 piece rear main what do i need or if anything to make it work in  my car with a 1 piece.  I heard i would need to change the flywheel and oil pan over but is that all.  Any help would be greatly appreciated Thanks Michael

Answer
The mains don't affect anything. If your buying a whole new engine to put in the car it doesn't matter. If you put a whole new motor in it doesn't matter. The old one goes with the old motor. If I didn't understand the question or answer it to your liking get back to me with a follow up.