i have an 85 that was originally carburated. i swapped it for 85 efi and took it to the ref. he told me once i got there that i didn't need to being the truck came with the option of efi. in your case though, the efi is different. i think it depends on the smog tech and whether or not he knows the difference between what the 85 and 91 efi setup looks like. call the BAR and ask. even if you did decide to run the engine harness from the 91, you would still be looking at swapping out a few things under the hood like the coil, ignitor, distributor, etc. sorry, its been a few years since i did mine, but i think the body harness actually plugs into the ecu somewhere too. there is 3 plugs on the ecu, and i know the engine harness and body harness get connected somewhere under the kicker panal. i'll see if i can find my old post...
