[77Birdman]

I would hit the first coat with etching primer. Then a couple of coats with the filler primer that you have. After the first coat of filler primer, sand most of it off, leaving enough to fill the pitting. Repeat second step a couple of times until the base is pretty smooth. Then you can top it off with some colour. Rustoleum products should be fine if you can find a colour close to original. I would do the letters/numbers in their colour first, then tape them off and do the base colour. Make sure you wash the evaporust off good before you start. I think it just needs clean soapy water.