sandblasting rear brake calipers, what do I watch out for? Options

[914 RZ-1]

I am rebuilding my rear brakes. I've taken everything apart, cleaned them with Simple Green and am currently soaking the parts in Evaporust. However, I might need to sandblast them.

1. Anything I should know before I proceed?
2. What to plug/tape up? I'm assuming all holes and machined surfaces?
3. What about the area in the caliper where the piston goes?
4. What blasting media should I use? I have some dull aluminum oxide I've used several times.

I've looked on the 'Net and found a few tidbits, but nothing specific to 914 brake calipers, so I thought I'd post here and see if anyone had any experience, tips and advice.

Thanks!

[914 RZ-1]

Here's a photo of the cleaned parts. I've labelled the areas I think I need to cover with tape:





A are mating surfaces, so it seems those need to be kept smooth and flat.
B may not be critical, but they are mating surfaces so...Any thoughts and comments?
I'm mostly concerned about the piston bore area (area C). According to the PMB document linked above, this area will be plated, so it needs to be cleaned.