No adhesion promoter required on metal. Stripper can be used however I would be sanding afterword and doing any body work. I would suggest a good quality automotive primer followed by wet sanding. Now you are ready for top coat, single stage or two stage, base coat clear coat, or ant other automotive quality paint.
Check this thread, cart was done with base coat clear coat, I added multi color flake to the clear coat.
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https://www.buggiesgonewild.com/showthread.php?t=107