I just read a post about seeing if the recalls on Fieros have been done, and I wonder how might the fact that my engine was replaced affect Pontiac's willingness to do them if they haven't already been done? It's still got the 2.5L, but it was replaced (it doesn't appear to be a novice job) before I bought it. By the way, I read somewhere (haynes manual or online maybe?) that there would be some kind of sticker under the trunk lid if the car had been serviced for a recall. Anyone know anything more about that? Mine has no such stickers.

Call your local Pontiac dealer and give them the VIN # of your Fiero. They can look ith up to see whether or not the recall work was done. Since they go by the VIN and not the engine, I don't see why they wouldn't do the upgrades, if needed. They may have been done as part of the engine replacement, if you can get in touch with the previous owner to find out.
The recall items are listed by year and can be found if you just look up Pontiac Fiero on the web.