What year is your replica? The '85-'86 Fieros with the 2.8L V6 utilized a 'Fiero' decal on the plenum. The decal is easily removable and anything you want could be put there. If it is an '87-'88, then it should have a plenum with 'Fiero' engraved, which is a little more difficult to modify.
Early Style
Later Style
Note that the surface area is not that large on the earlier style, meaning that whatever plate you place onto it will likely be larger than the ridges underneath. As mentioned there are some outlets that offer and have offered replica plates, but some have them custom made.
I will say that the engraved plenum is typically more valuable to Fiero owners than the non-engraved one. I recently swapped my '86 GT's for an engraved one, so if you do have an engraved plenum look to offload it for some cash before you modify it for your replica.
Additionally, if you look above the MAF, you'll notice the brake vacuum hose protrusion is a different size. On the engraved ones, this can be removed as it's threaded. However, on the non-engraved it cannot. The size is a large enough difference that the hoses cannot be switched between one another without issues.
[This message has been edited by Fiero84Freak (edited 03-17-2011).]
