I'm looking for any info on what certain parts were painted from the factory. I believe the frame itself was semi-gloss black, but I'd also like to know what colr to paint
-any suspension components
-the car's underbody
-engine compartment walls
-engine components
etc.

Thanks for any help!

Well, since nobody else stepped up,
try:

amesperformance.com

performanceyears.com

Both are restoration houses for Pontiac-specific pieces and information. There are a number of good books documenting GTO. These shops sell the books.