wlecome
As you will find out, most anything mechanical from other G-Bodies will swap. Chevy S-10/GMC S-15 Sonoma up to at least 92 (maybe 2002) will use the same suspension parts (2WD only of course). As a quick list:
Sheetmetal - 81-87 Grand Prix. Does NOT interchange with other G-Bodies. Check eBAy and junkyards. I need a door and cannot find any aftermarket support. 78-80 sheetmetal was different.
Dash- Any Pontiac G-Body from 78-87 will have the same dash. The cluster bezel for a 78-81 will fit, but has a hole for the wiper switch. 82-87 does not have this since that was moved. My opion is that Pontiac had the best dash of all G-bodies. Again, junkyards and eBay.