Matt, like ltdrider says, walnut shells are probably the best. At least they're bio-dregradable.
I've had several cases blasted with #8 glass beads that work quite well. Again, the media will get everywhere if you don't have a cabinet.
As far as the outside of the cases go, just blast away. However I try to refrain from blasting gasket/bearing surfaces for obvious reasons. When finished blasting, I like to blow off the blasted areas with compressed air.
One thing that MUST be done is to take care of all the bolt holes. I blow out all the media that I can, then use the appropriate tap with some heavy grease to clean up/clean out the threads.
Then I use carb or brake cleaner to spray the cases down (and into the bolt holes) to remove all the media and grease residue.
I am going to paint my engine with PJ1 black engine paint because I don't have the patience or know-how to polish and polish and polish, etc.
Eastwood Company sells a product called ZOOP that supposedly keeps bare aluminum from oxidizing, but I have yet to use it. From what I understand though, the ZOOP coating will only last about two years. Then it seems you will have to do the process all over again. Again, not for me.
I wish I knew what Kawasaki uses to keep their cases shiny for so long.
I hope this info helps and good luck to you. Keep us posted on your progress.
Jim