I am finally getting into the bodywork on the 57 GMC 370 LCF.
I am very surprised, there is only one coat of paint, very thin now. Looks to be the original paint, never re-painted.
With just a small amount of sanding and you are to bare shiny metal. I have not found any signs of a primer coat anywhere.
Since GMC's were built for work back then, think the factory just said heck with primer??

57 GMC LCF 370
55 John Deere 40-W
59 John Deere 430-W
2000 GMC 4x4
56 John Deere 420-W
Pix on Photobucket