IMHO the only way to go is shoot the bare metal with epoxy primer. This will allow you time to do whatever you want, when you can get to it. In the areas you have to work on (leading, welding, etc.), grind down to bare metal, then do your work. After you finish the work, Duraglass/Glaze coat if you have to, then shoot a self-etching primer on it. You'll be good to go until you're ready to primer the entire vehicle prior to painting. Then you will have to scuff the entire surface prior to priming.
