Charlie asked me to weigh in, here.
One thing that I seem to remember was that Felpro got it wrong. The 87-88 Fiero gasket kit had the wrong water pump gasket.
I don't recall if it also had the correct one, or if I had to buy a separate water pump (and maybe timing cover) gasket kit. Seems like I had to buy a separate water pump gasket, at least. (Sorry... It's been 5+ years.)
Edit - The gasket that you have on the way, at the bottom, above, is the right one.
Regarding casting numbers...
The iron 2.8, 3.1 and 3.4 heads are completely interchangeable. They are all an identical casting, even if the numbers are different.
The only difference is that the 2.8 NON-HO heads (which came on carbureted engines) have smaller valves.
Any head that came from an EFI engine, including TBI EFI, should have the big valves.
The heads that came on the X11, should also be the HO heads, even though it was carbureted.
The 3.4 block is its own beast.
The 3.1 is a stroked 2.8. It has a different crank and different pistons from the 2.8, but it has the same bore size.
The 3.4 uses the 3.1 crank with a larger bore. All rods, for all displacements, are the same. This supposedly includes the rods in the 3.4 DOHC.
The 3.4 Camarobird block (the one that "shipped" with iron heads, that we are concerned with) can be identified by a large "F" cast into the side of the block. This may hold true for the HT 3.4 crate motor, too, but I've never seen one of those up close, so I can't say for sure. It will have a cast pad on the right (trunk) side, that would usually mount a crank sensor. It's unused on the Fiero, so you may find a sensor with clipped off wires, or it may have a metal plug driven in. Same with the cam sensor. On the F-body, it was located on the horizontal surface, just above the timing cover. On the Fiero, it will either be plugged or "clipped", as before.
Since you have an aftermarket cam, you probably don't care about this, but it's probably worth mentioning. The 3.4 Camarobird cam has the identical specs to the stock Fiero cam. IIRC, it's .394(I), .410(E). The only difference is that it has a tab to trigger the cam sensor on the F-Body.
If your block has provisions for a roller cam, it is a FWD block. NO RWD applications of the 3.4 came with a roller cam.
The FWD block might seem like a good idea, but the FWD pistons (which were designed to work with the aluminum heads) will yield about a 7.5:1 compression ratio. The correct 3.4 pistons should be mostly flat topped, or have a moderate (~1/8" dish.)
Lou Dias on Pennocks is using a converted FWD block in his Fiero, in the event that you want to search out his threads. It sounds like it was a bunch of trouble to do.
In reality, that's probably NOT what you have.
If you have any specific questions, please feel free to ask. It's been a while since I did mine, but I still remember a few things about it.
If I don't answer, please feel free to PM. Sometimes it takes me a day or two to come back here. I'll get notifications of PMs.