my dad had one which was a 88 the last and BEST year of the car. he had the FORMULA model basically the base car with the top end model car's aero front end and the 2.8 V6, interior, and better (LOTUS designed for 88 year only) suspension. it was a blast of a car, the only thing he did not like was it was an AUTOMATIC but he could not find a 88 coupe, formula, or a GT with one. it is a little known fact that ANY transverse GM Front Wheel Drive drivetrain will drop in the back of the car being it used the early 80s 'X' platform which was the basis of GM's early front drive cars of the era. I have seen Fieros with the following drivetrains.
300hp 'northstar' V8 from a Eldorado coupe with nitrous (car had over 400hp when system was armed
)
2.4 'quad 4' hooked to a 5 speed from a Grand Am or its Olds 'counterpart'
2.4 'ecotech' inline four from a cobalt
3.8 (3800) supercharged from a buick park avenue ultra
3.4 Twin Dual Cam V6 from a cutlass supreme or lumina z34
of those the supercharged 6 from the buick or the nitroed northstar are my favorites. my dad said he thinks the current small pushrod V6 that is in many impalas and montes (like mine) would be a great motor for them you get 160 to 180hp depending on the size. I personally think the 3.6 DOHC V6 in the new malibu or the Direct Injected version that will be in the upcoming Traverse SUV (with 300hp mind you) would be the best motor to put in the back of the car.