Two problems, never sand blast on exterior body panels you will warp them so fast it will make your head spin. The second is POR is not meant to be used on exterior panels. Its meant for panels like floorboards and turnks not the topside of a hood.
I would grind off the paint and see what is under it. As you guessed there will be some pitting but you should be able to rid most of it with the grinder. What ever you do dont continue to grind til you remove the pits, you will have paper thin metal. Use a drill and wire brush or wire well to get into those pits.
Once the ALL the rust is gone use a self etch primer to seal off the metal. Self etch is not expoy primer, totally different and much better at fighting corrosion. Then apply your primer surfacer or more commenly called 2k primer. Some good self etch would be PPG dx1791, Dupont variprime and sherwin williams GBP980. 2K primer would be PPG K36, Dupont europrime or something like that, and S-W ph48...Eric
------------------
1970 chevelle
1970 chevelle SS455 not a typo its a BUICK BABY
1949 and 1972 chevy trucks
http://briefcase.yahoo.com/bc/sevt_chevelles
