I used a grey Rustoleum Hammertone paint on the interior of my '64 with a topcoat of flat clear. The only problem I had was that the thinner metal, like the ash tray, had a much smoother texture than the dash and cab which were thicker metal.
http://i305.photobucket.com/albums/nn214/jfnar/1964%20chevy%20truck/79bb3aa7.jpg


'64 swb stepside (gone)
'57 1 ton
'53 phone truck
'59 swb
'46 1 1/2 ton
'68 swb gmc