Modern 318 in a 72 duster.. Possible???

You can (and I am not saying that it is easy) swap in the engine and transmission from the Jeep along with the computer. That way, all of the drivetrain will work together as it was intended. With everything controlled by the computer you would get maximum performance, mileage and reliability.

Then for performance you can add a chip!

I am not certain about the Jeep transmission set up though. For the swap that I think you are looking at doing, I would look at either a Ram or a Dakota pickup for a donor... a 2wd donor will work better than a 4wd donor.