Oil pan, bellhousing and heater housing for sure. On the others, just make sure nothing is sandblasted that has moving parts, like bearings or bearing races, that sort of thing. Electrical tape is pretty resistent to sandblasting and glass beading, so you can cover areas you are worried about, if you don't shoot them directly for a long time...be careful those areas will be missed.
Also make very sure you remove ALL the sand from your finished pieces. I ususally pressure wash all parts a couple of times, even if this is with a pressure nozzle on a regular garden hose, then blow them out REAL good. Don't want sand where it doesn't belong. Wash, blow, wash blow, inspect.
