If he has the ENTIRE 1988 harness, he can swap that into the car. I'm talking engine, body, trans, doors, etc.
Otherwise the easiest solution is to get a 1993 5.0 EFI engine harness and plug it into his current 1993 body harness.
The 1994 stuff won't work. Too much changed between 1993 and 1994 in terms of how the car is wired. In fact, the 1994 engine won't work as is either. Youll need to change the accessory setup to the fox style, and change the intake/TB assembly to fox style as well.
You can make this swap work, but you don't have the parts. Hate to say if but if you don't have $100-150 or so for a 1993 engine harness, you might not have the funds to complete the project with all the other little odds and ends that will come up.