If you're preserving patina, it looks most accurate in satin or flatter finishes. That can be done adding a flattening agent to a gloss paint, or buying a satin/low-gloss finish.
30% flattening is a good ballpark. Shoot a test panel, note your mix ratio, use proper mixing cups with ratios marked.
Prep: clean & degrease fully, follow up with wax & grease remover, scuff with 600/800/red Scotchbrite for mechanical adhesion.
Take your time & be thorough on the prep & masking.