I have yet to find anything definitive about piston angles (the standard 20 deg) on the 930 calipers, but mine have been noisey for about a year since I replaced the rotors and pads.
So I pulled the pads on one of the front brakes today and found that the leading piston on one side was at about 20 degrees, while the other pistons were all vertical.
I did some searches here and on Pelican and found:
http://forums.pelicanparts.com/showt...threadid=90849
and
http://vintagebus.com/howto/brakes/rebuild/ (pics of rebuild manuals)
Also, if I want to turn a piston, what's the best way to do it without damaging them?