I wanted to spray the firewall before I put the engine and tranny in our 66 Burb. Like you, I will have a body shop do the main body and spray work, because I am anyhting but a body man. I wound up buying a $30 HVLP Gun from Harbor Freight, and used I believe the brand name is Omni single stage paint. The numbers cross reference to the PPG color charts for the inside and out. I painted the firewall and the wheels, and I was amazed at how good it come out. It just flows together afterwards, and it has a gloss and flatness, that is probably way better than I ever needed. You would probably get better advice from the "Paint" forum here, rather than this one, but that's just my 2 cents from someone who does not do it all the time.
