You can use that Tranny, but I believe you will need an adapter plate.
You will also need to figure out the shifter, bcc this Tranny is out of front wheel drive cars, so the shifter on the tranny end is "backwards" for a Fiero.
I just installed a 5 speed getrag out of a 91 Sunbird and used Dickman's kit to convert it from FWD to RWD.
But yes it's possible.
P.S. you might also have to figure out a slave cylinder mod...im not sure if the Fiero Clutch line can hook up and work directly with the F40's slave Cylinder or if you need to rig something up. Im sure someone on here should know.