i'm running a 28 tooth. some grinding had to be done, the case was still intact though, just take your time and don't get too aggressive. i had to take away maybe 1/2 of the thickness of the case.
in a somewhat related note, i was riding the other day, my master-link broke and the chain whipped and cracked the case to pieces... do i need to keep that case on there? how will it run without that whole piece on there? should i jimmy some cover for the flywheel?