paint choices
Ain't America great? You can get a hundred different opinions, but the only one that really matters is yours! Lacquer, Acrylic Enamel, Urethane, Basecoat/clearcoat.... Of course, in some locales (Calif especially) you are limited by what is
permitted.
The Basecoat/clearcoat system wasn't around when I (well my buddy did the actual spraying) painted Alpha Cat. Go ahead and look at the pic I had posted earlier. That was Acrylic Enamel with a Urethane clear put over it. That is a metallic gold (paint code 6F) That paint job was done waaaay back in 1984! It still looks good today, although I'll have to admit that the car has been apart in the garage since 1985. At least the paint still looks good!

Back then, you could get a
gallon of enamel for under $40. Nowadays, a half-pint of Basecoat costs more than that!
All of the cars we had restored/repainted back in the 80s were done in Acrylic enamel. Lately, they all have been done in BC/CC though. The most important part is getting your Cat straight to begin with. I spent an entire week block sanding/ prime/ block/ prime/ block/ prime... well you get the idea. There isn't a ripple or wave anywhere in that paint, I can assure you!
Nowadays, the best paint for the engine compartment and underside of your Cats is going to be the two-stage black epoxy primer, if you can still get it that is! It has the right flat sheen, is impervious to most chemicals, and wears well in the underhood environment.
Have fun!