Choices
You have a good start in a properly prepared frame, taking her down to bare metal. I have done this differently over the years, depending on the application (whether I wanted it to look "factory correct" or "just plain functional".
The first X frame I did I sandblasted the parts, used a "metal prep" solution (that is basically an acid that etches the bare metal, giving it some "tooth" for subsequent paint), then applied POR-15 using a brush. That's right, a brush! POR-15 is a product that can be applied over bare metal (they say rusty parts as well) that dries to form a hardened sealer/barrier over the metal. Following the instructions on the product, you clean the bare metal, then "etch" it with Metal Prep, then apply the paint. You can spray the POR, but I recommend using a brush, less apt to get it in your lungs (it's nasty stuff!) and the result is a smooth finish. I used Eastwood's "Chassis Black" over the second thin coat of POR, just before it sets up.
The second frame I did I went exclusively with Eastwood products, using their "Rust Encapsulator" in the place of the POR above. I prefer the POR over the Rust Encapsulator, as the latter didn't "flow out" as well and left some brush marks on smaller flat parts, such as the A arms. As before, I top coated the frame using Chassis Black from Eastwood products.
Neither of these is even close to what the factory did, which was to lightly dust the frames with flattened semi-gloss black paint (semi-flat?), then stack them on rail cars and let them sit out in the elements before assembly
If I were to do it again, I would use a hardened single stage enamel on my frame, such as those in PPGs product line. I did this with my inner fender panels, pulleys, brackets, small pieces like that, and the results were excellent! It is more resilient to fluids, spills and "wrench bumps". The Eastwood spray bombs are not. Brake fluid immediately curdles the spray bomb products (at least that is my experience). It does not affect the POR, and I suspect a hardened enamel could withstand brief encounters with nasty chemicals.
If you can figure out how to correctly "flatten" the black enamel, you would have achieve a "close to the factory" look with good preservation potential. I worked with my local paint store to come up with a mix that GM used in the early 1960s, taken from a mix my friend did on a 1964 GTO. Good results, maybe a bit on the glossy side, as we didn't get enough flattener in there. Hey, it's my car, I like it!
Good luck in making your decision. We can steer you towards these products and their vendors if you would like to know more. Always read the labels when using the products, and if you spray, protect your lungs, these are dangerous mixtures!
Cheers,
TomK
I meant to say DP-90, in other words, low gloss black