I have a 1980 eldorado with a 368 big block in it.

I want to swap it for a olds 350.

I found a 1979 eldorado with a diesel olds 350 that has been converted into a gas engine. well over 150,000 miles on it.

What should be the correct process to swap engines?

Should I remove the engine and then rebuild 350 engine and then replace into the 1980 car?

Can i use existing transmission in the 1980 or should i swap that out with the donor engine?

Thanks for your help.