I've sand blasted an assembled guzzi, 750, and MG TD engine. All with no problems. Just have to very securely plug exhause, intake, tach, and oil ports. The thoroughly clean it off after. They all have a LOT of miles on them since, no problems.
I painted the 750 and MG TD engines, left the Guzzi engine raw. All is well.
I also soda blasted some wheels. It's more expensive but a viable option and will not harm anything if by chance it does get in the motor.