Magnum engine from 1992-95 are OBD-1 and used a hydraulic 4sp transmission with converter lockup and overdrive toggled on/off with a simple 12v circuit operated by the ECU.

96+ went to a fully electronic transmission and OBD-2 at the same time. For this reason neither the electronics or transmission will swap between 92-95 and 96+.

The BEST thing you could do is swap a 92 dakota engine wiring harness into your 91, and hope and pray the connector at the dash stayed the same. Alternatively you could swap out all the wiring(dash board, lighting, etc) if you wanted to avoid rewiring stuff.

I used a 1995 harness/ecu for my swap, I found the engine wiring harness section is remarkably self-contained once you gut out the lighting, abs, etc. All that's left to hook up is a power, ground and a keyed power. You will need a speed sensor hooked up or you will stall on decel.

The early magnums will want around 35psi of fuel pressure. The TBI's were more like 14 and the 96+ units went to 55 I think. Oblivious to this fact, I first installed a 55psi GM LS-1 fuel pressure regulator/filter because they are easy to retrofit to just about anything. It ran, but rich so I put smaller injectors on to compensate.

The OBD-1 computer doesn't care what transmission you put behind it, so long as its hydraulic. If you put a 3sp behind it, you may get a code for overdrive and lockup circuits open, however it won't affect driveability. I have a stick shift so I found a stick shift ECU for mine so this isn't an issue for me either way. If memory serves, the OBD-1 magnum ecu does have a circuit that tells the ECU if you're in gear or not, however I'm not sure what the function of this is, perhaps to cancel cruise control if you nudge the shifter into neutral?

You will have to transfer over your LA sensors for your dash gauges to work. Also I wouldn't expect the a/c connections to be the same but not sure on that as I don't have a/c in my swap.