I realized last night after this came up that I was actually more worried about the protruding o-ring issue than I had realized, so I talked to Chris Mulhall (top-spinner, yo-yoer, CAD expert) who did the CAD for me. Apparently I forgot that I had already had this freak out, because he told me that the groove for the o-ring was already deep enough that it will not stick out at all. Whew!