If it were me.......
I'd use a heavy abrasive, such as sand or aluminum oxide and blast it nice and clean. You have to use a hard media like this to get down in the pits.
Then, I'd use a filler like All-metal to fill in the low spots, then smooth it out and sand/grind to desired level of smoothness. Then you can use a good self etching epoxy primer.
I have access to a good price on gallons of Southern Polyurethane's line of epoxy primers. I can get you some and you can pick up at the Ga Rally if desired.
Alternatively, you could use plastic filler, but I prefer the All-metal (years ago was known as alumalead). Made by Ditzler.