318 4bbl to FI ?

My son has an 84 D150 with a 318 4bbl. All fine and dandy down here where we don't have smog checks, but he's moving to a state that does have smog checks. I'd like to do some work to his truck and bring it up to him. How difficult would it be to slap another engine in it with fuel injection? Assume that I have access to a junkyard with plenty of FI engines that come complete with wire harness and ecm. What would I have to do for a swap? I'd rather not change anything on the 318 because I was thinking of taking it out and using it in my 72 Dart, replacing my slant.