The best thing to do is go to a local transmission parts supply source and purchase the update manual for the four speed series usually about $17 that will list the gear ratios and torque converter stall speeds. The book is by a company named ATSG I believe, mine is at a relatives house so I can't help with the info.
My understanding is that the strongest would have been in a Caddilac but it is possible that in the later years all in a particular series carry the same ratings and updates.
Make sure you get the decoder information so that you have the right gear ratios for the type of performance and fuel economy you desire, since you will have a very powerful engine in stock form relative to the 2.8 you may want to lean toward the low side in stall on the torque converter which GM has OE applications going as high as 2700 stall for some of the four cylinders. That would be great for racing launches if you could get the traction but for normal driving possibly a bit excessive. I would opt for a 3.42 final drive ratio and about 1800 stall which I believe is about the happy medium point for fuel economy and performance, that should push you close to 30 MPG and still keep your 0-60 times in the 5 sec range.
I've owned a 3.23, 3.42 and 3.73 rear axle IROC, 3.42 replaced the 3.73 when the ring gear droped a tooth, cars which weigh about 600 lbs more than the fiero and are not as aerodynamic that still managed around 25 MPG hwy. The 3.73 was a blast to drive with the stock converter with a stall around 1800 with the moded 305 TPI and later 383 TPI but that was with a 16 gal tank and gas prices in $1.07 gal price range. If you commute 30 miles one way which I did at some point for school and work economy becomes an issue.
