Your car had enamel paint applied from the factory, unlike General Motors which used lacquer in some factories up to the early 1980s. You shouldn't have problems with recoating with new enamel.
It's likely to be alkyd enamel, although it doesn't matter. You're spraying enamel over it so as long as you are have sprayed enamel before just do what you do.
I have a 1 1/2 gallons of 68 TT1 laquer available. I think it is close to F5, have to check
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Your car had enamel paint applied from the factory, unlike General Motors which used lacquer in some factories up to the early 1980s.
Don't spray lacquer over that unless you really crave adventure