98 Bravada Engine Replacement (USED)

I have a 98 blazer that i need to replace the engine in. My question is i have found 2 motors one out of a 97 with 86,000 on it. The other out of a 01 Silverado with 63,000 on it ( I can crank it and hear it run before i buy!) Which one will be direct swap? I have the motor with the the CPI but the square upper intake( TB bolts on top). I really want the newer one but dont know if it will go in with minimal changes. Or if it will even bolt to my tranny. I understand that since mine has AWD, i have to swap oil pans but is that it? Do i need to swap pick up and screen? Or just the oil pans and good to go. Also what about the headers? Will my current ones bolt up to the newer 4.3? I have done a little research but i have to pick one or the other by tommrow evening, so i need a quick response and will continue researching! Thanks again.

I have a 98 blazer that i need to replace the engine in. My question is i have found 2 motors one out of a 97 with 86,000 on it. The other out of a 01 Silverado with 63,000 on it ( I can crank it and hear it run before i buy!) Which one will be direct swap? I have the motor with the the CPI but the square upper intake( TB bolts on top). I really want the newer one but dont know if it will go in with minimal changes. Or if it will even bolt to my tranny. I understand that since mine has AWD, i have to swap oil pans but is that it? Do i need to swap pick up and screen? Or just the oil pans and good to go. Also what about the headers? Will my current ones bolt up to the newer 4.3? I have done a little research but i have to pick one or the other by tommrow evening, so i need a quick response and will continue researching! Thanks again.

The salvage yard interchange book should have that info.

All 4.3 v6 should fit transmission.
But other stuff is where the rub may come in.
Good Luck