I never sandblast i.e beadblast calipers anymore. They get stuck in the seal grooves threads, back in the piston body, everywhere and it is a nightmare. You are asking for trouble. If you dont spend 15-30min per caliper cleaning it 4 times over.
If you really want then you should just blast the caliper with the piston body complete and with slide pins threaded on.
If you really want then you should just blast the caliper with the piston body complete and with slide pins threaded on.