[Raptor]

You could sandblast it as long as you were very careful to stay off the machined surfaces. Personally, I wouldn't do it that way, there are chemical rust removers that will work fine and be less dangerous to the block. The other thing to consider is that the paint work should be done after machining and as soon as the block is hottanked, it will rust again pretty quickly. I always have a bit of clean up to do when they get back from the machinist.