We've blasted a number of assembled items, from engines in frames to wheels on or off bike, with a variety of media. Some efforts were definitely more redneck than refined. The masking work is usually not fun and no matter how much you try, it's hard to reach everything on an installed engine to blast it well. The residual abrasive concerns have already been addressed, so no need to discuss that further.
The consistent issue across all efforts was that anything aggressive enough to remove paint (but maybe not corrosion or rust) or clean alloy will also remove any rust- or corrosion-resistant coating on ferrous metal components. Then they rust like crazy. Even bikes with ss hardware generally have some plain ferrous parts. So after blasting, you have to r&r or exchange the fasteners, be an anal-retentive hero cleaning them in place before clear coating every one of them so you can wait to see which one(s) you missed or just live with a cleaned wheel/engine/etc that's got lots of bits of orange rust growing everywhere. You can just wash everything well and clearcoat everything, but that's a quick fix- not a real solution. It really depends upon what you deem as acceptable or how much time & work you will invest to do it the "easy" way instead of doing it the way that you know would be best.
There aren't any magic shortcuts.
