Were the radiator fins originally painted black by Ford? From the look of some of the old photos, it would appear so.
I believe they were, but don't forget that radiators require a special paint, not your run of the mill, off the shelf paint.
Why? What would happen if you do use rattle can paint? Seems like I did this on my '27 years ago and it seemed to be fine. What kind of paint is required?
They do make paint specifically formulated for radiator fins. It's designed to go on thinner so as to not goop up the fins and thereby diminish heat transfer. It is available in rattle cans.
Eastwood sells it
If you paint at an angle to the fins top and bottom, rattle can paint works fine to paint just the front outside and bottom tank. If you are painting the whole radiator use the correct paint.