I used GM Restoration Paint, or sometimes called Chassis Black. I don't have the can in front of me, but a quick search shows it to be GM part# 1050104. It can be hard to find and word is they changed the formula to be flatter than when I used it. This company appears to have it in stock and it's sold by the gallon: http://www.melroseheaders.com/
I just used a can primer underneath and after 8 years, it's holding up great. Spraying will get you the best results. I am not sure if this is correct if you're going for an accurate restore, but this should make it look nice.
