Painting Dart Grill

I am going to paint my 70 Dart grill with base/clear. I already have a black I like and I got a Chrysler Silver that I like. (I know it's not argent, but it will still look good.)

My question is, do I need adhesion promoter because it's plastic or will a good cleaning, scuffing and wax and grease remover do it well?
I would not worry about it. scuff ,clean and clean and clean. Use a good sealer.