None of them will be easy as you'll have to change the wiring, and computer to make it run, plus all the parts for a V8 to go in there, front of the motor, exhaust, it will be a chore. The wiring would be the biggest thing.
I know all that but what would be the easiest less mods and all that
Looks like the 5.7L would be a good candidate.
@Rowefast, I agree, my answer was to buy a Camaro with the motor you want. It would be probably be cheaper than having a shop do it for you. If it is a learning project which they are going to do themselves, have fun lol, and buy some Tylenol you will need it.
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