If you are looking to do a 3800SC series III swap; the easiest route to convert the drive by wire operation is to install a cable operated throttle body (use the ZZP adapter) and run it on a 1996-2002 PCM with applicable wiring.
My opinion is that the more state of the art current technology LFX engine would provide better performance naturally aspirated. Not many of them have been swapped into Fieros so far but I see them as the next popular engine swap. That engine is very light (all aluminum) and provides 300 HP stock. They are widely used on new GM cars and are still available new.
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "