Yes, the upper plenum flows considerably better than the Fiero item, so if you don't mind a non-stock look, go for it. There are starter mounting issues between in line and transverse installations but easily dealt with. The added torque even if you do nothing to the 3.4 is welcome.
I used that engine in my old British sports car. The added benefit is that it has DIS (coil packs) so you can ditch the distributor forever. You can get a late 80s era ECM to run it - it does away with the SFI aspect and goes back to batch fire, but that's no big deal. Easy to integrate into a Fiero system.
Here's mine, done up in MG colours and with the upper plenum re-engraved to suit. You may recognize the valve covers - if you use them, be aware that there is a contact area near the rear between the valve cover and underside of the plenum that needs to be dealt with. Fit them dry and then mark where you need to grind and go at it carefully until all is well. If you don't know about it, it is possible to stick it all together and then wonder where that big vacuum leak came from.
[This message has been edited by BillS (edited 04-10-2014).]