Easiest way to determine is there is any enamel based primer or paint is to take a small aerosol can of spray lacquer and shoot a few spots with it.
Sit back and wait a bit. If it is enamel the lacquer will start ruining itself and turn into a wrinkle finish.
I generally shoot acrylic enamel with hardener added. Most of my work has been on motorcycles and it holds up very well even being subjected to oil and gasoline.