You can take this with a grain of salt, as I'm only telling you of my own personal experience.
My first Fiero was an 84 (still have it
) with a cracked head on the 2.5 engine.
When I took it apart to rebuild it, I took the engine to a reputable machine shop to have the machine work done. They were the ones that told me the head was cracked and that I would be best served finding a replacement. When I asked what all will fit, they pulled out a sheet from GM stating that there had been over 100 changes made to the 2.5 head in a less than 10 yr. period, and that you had to watch what you used as a replacement, if you wanted to stay with "original" type specs. Most of the changes had to do with the "swirl" patterns in the combustion chambers and making "adjustments" in the casting to hopefully improve performance and efficiency.
To make a long story a little shorter, my search took me to the junkyards, where I eventually tested no less than 5 different heads, all of which showed cracking in the webbing between the intake and exhaust valve. I had the yards check their books to see if there were any other cars with a 2.5 that had a head that could be substituted. There were, but I don't recall all of them now, this has been 15 years or more ago.
I found a head from a 2.5 off a Chevy Monza, 79 I believe, which everybody said would not interchange. But it had a simple open combustion chamber, with no tapered "shelf" between the valves. I looked up the part number for the head gasket, intake gasket and the exhaust gasket..they were all the same part number as for the latter type head as was used on the 2.5 in the Fiero.
I decided to go for it. I did have to switch the thermostat from one end of the head to the other, which involved removing two freezeplugs (small inner and larger outer) and moving them to the other end of the head along with the thermostat housing, which also had to have a little bit ground off one of the mounting ears to fit right, but other than that, it was a direct bolt on. I drove the car another 15,000 miles after that, then the tranny (auto) went out and it got parked, as I had acquired additional Fiero's in the meantime.
Point being, there were allot changes to the head and sometimes you have to go beyond the book.
Like I said, just my own personal experience.