So i have a 91 si hatchback stock engine . I just picked up a 88 hatch with a gsr obd2 engine in it, the wiring is a nightmare in it so i can't use that. I made up miy mind to just save up for a aftermarket harness, but was curious to see what others have done in a similar senario.
I also had in mind of swapping out all the mani, dizzy. alternator etc (im probably missing more ) and then just using my si harness. Also have been reading that obd-1 is more preferable.

 

A stock 91 Si running, is much better than a nonrunning GSR swap mess. Keep your Si the way it is.
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I intend on leaving it in there until I have everything ready for the swap.

 

Junkyard. Get replacement harness to give you a second start.
Would not recommend the 91 si harness in the 88 unless you are changing out the engine and cabin harness.
Besides, the 91 runs... why would you even think of touching it???

 

I bought the 88 only for the engine.

 

Then your post is a little confusing to me.
Now I guess you are saying that the plan is to take the engine from the 88 and swap it into the 91.

Easiest method is to get the OBD1 jumper for the 91.
Convert the IABs on the GSR to work with the OBD1 trigger (relay to convert 12v trigger on OBD2 to ground trigger for OBD1).
Do the resistor box delete so you can use the GSR injectors.
All the OBD2 sensors (distributor and all) will work on the the OBD1 ECU.
Can use a stock OBD1 P72 ( -or- a chipped OBD1 ECU+ IAB conversion with a P72 basemap).