I'm going through this very situation right now.
Here's what I DO know:
*The five speed Getrag is in reality a Muncie transmission
*A Fiero Getrag (Muncie) should bolt right in to replace the four speed
There are FWD versions of the Getrag (Muncie) that can be installed in the Fiero, but require some additional work. Visit Rodney Dickmans' website HERE
He sells components to assist in the installation of FWD Getrags. It seems the primary hangups are in the shift linkage and cable brackets. He also mentioned in his article at the site above something about the speed sensor.
*While I haven't recieved any confirmation one way or another, I assume (yeah, I know, I know) that the shifter assembly needs to be replaced. Being that the four speed shifter is regulated by the transmission, I wondered if it wasn't possible to modify the four speed shifter, but I'm thinking that probably won't work. I've put out feelers here to obtain a shifter, but so far no one has made any offers.
Hope this at least gets you started in the right direction.
-Taiji
[This message has been edited by Taijiguy (edited 07-12-2000).]