NuMetalgamer

So I'm just starting to learn more about mechanics (I'm more of a computer guy myself) and my uncle has taught me to like Mopar cars. I'm looking at buying a 1974 Plymouth Duster with a 3.2l engine. My question is how hard would it be to put a much bigger engine in there. Is there any issue with it fitting at all or is there anything else I would have to worry about. Like I said I'm really not familiar with anything so any help would be appreciated.