Yes, IIRC all transmissions that came in the Fiero have the same bolt pattern as the 3800. The muncie (which is your transmission) also happens to have the strongest casing that was put in the fiero. Of course, you won't be able to abuse the trans too much because the power will break it. For in town driving, the 4 speed is probably the best way to go because of the gearing. If you drive on the high way a lot, you might want to consider upgrading to a 5 speed F23 trans.
BTW, welcome to the forums!
[This message has been edited by zzzhuh (edited 06-10-2015).]