I stripped the paint off of my '54 radiator with lacquer thinner, a tooth brush, and a bunch of paper towels. I didn't try to strip every last bit of black paint off. The brass is not polished show-quality brass. It has pits and stretch marks that easily fill with paint when painted, but that will look rough if top coated with a clear coating. I painted it with self etching primer and buffed with a ScotchBrite pad when dry. Then I painted with rattle can Rustoleum #7798830 Protective Enamel Semi Gloss Black. Rustoleum #209584 Automotive Aerosol Semi-Gloss Black has the same sheen.
I didn't strip or paint the fins on the radiator.
Even if you can polish the radiator to a mirror finish, I don't know of a product that will keep it "bright-white-brass" color. Most products will allow air and moisture to eventually penetrate to the brass, corrode it and change the color.
Radiator in my 1954 3104:
> Fully stripped> Top (1)> Top (2)> Radiator "paint booth"> Newly painted radiator - rear view> Newly painted radiator - front view
