If you want the alternator to be worth anything, either for a future restoration of the car or to sell, don't sand blast the case halves it will ruin them. The only reason that these things are worth any kind of money, or as a correct piece for a car, is due to the numbers that are cast into them or stamped on them, sandblasting will ruin those numbers. If you decide to rebuild it then go ahead and sandblast it and rebuild it but, it will be worth less than any other rebuilt alternator from the parts store as it will be the same thing only without the warranty. Now if you decide to restore it, there is a difference from rebuilding it, then have the parts vapor honed, that will clean everything as good as sandblasting but it will leave the detail that you need for a proper restoration. Dixie Restorations, at the link that Sixpaksteve put up, does amazing work and it will be perfect when they're done, a basic restoration runs $325.00 if I remember correctly. Plum Crazy Garage does incredible work also. Just some things to think about.