While sandblasting the frame on my 1.5 ton truck I notices that the original finish under all of the brackets was black. I have also seen factory photos that show the frame and sheet metal in a black finish from the supplier.
I did read the paint FAQ at
http://bobstory.tripod.com/faq.html but my year of manufacturer isn't really clear... best guess: Acrylic lacquer (black)????
Any idea what type of finish it really is?