replacing engine in 94 caravan with a 91 engine

how hard would this be, I posted earlier about a drivers door, I can get a van without engine for the same as the cost of the door, and I am wondering if it would be worth it to change over the engines? I am not even close to being car savy not even matchbox car savy! I know to put in gas and oil, but am wondering if would be worth my while to do this! HOW hard is it really, could my hubby do this he has replaced engines but not in a mini van. (i might be afraid to ask him a bit before I find out how hard it is) I am a bit of pain in the butt!