Yes you can use the factory computer. Your 94 is OBD-1 and it is quite simple. I put a 5.2 magnum into my Jeep and I used a 95 donor harness and computer. To do this, I installed the engine and transmission into my carbed jeep, then I took the 1995 wiring harness and peeled it apart. I found the part that controls just the engine is remarkably self contained and really only required me to hook up 3 or 4 wires to my factory carbed jeep harness.

For you, if you don't mind swapping cabs and boxes, you could put the 71 cab and box onto the 94 frame. While you have it apart I would peel apart the 94 wiring and keep only the engine wiring and reuse the rest of the 71 wiring.

Alternatively, you could transplant the 94 engine/trans/engine wiring+computer into your 71 much the same way as I did the swap on my jeep.