Can you blast easy? By that I mean with a moderate amount of restraint. If so just dust off the remnants of paint, especially in the pitted area. Next step, get a rattle can of SEM self etch primer. It contains a mild acid and "eats into" the metal for a strong bond. Within 24 hrs of application you can go right to your surfacing primer, I prefer to prime within 1 hr of self etch application. Once etched and primed you need to sand the pitted spots well and apply a smooth filler such as USC "Icing" or Evercoat "Metalglaze". Sand all of it to level and don't look back. Notice I didn't advise that you keep laying on coats of surface primer. All that will do is give you too much build, enough that it may even crack as you install your nice freshly painted part. If it doesn't crack on installation, give it few heat cycles and it will. That diecast moves a lot with temp and new paints are sensitive to excess application. This is a job where less is more, especially in the hard substrates.