Mine has an exposed lower pivot bolt but the cage looks identical and measures 53mm c-c.

The 30t has me excited. I've got a set of 10spd campy downtubes on pauls thumbies. Combine this with an 8spd campy RD and I should be able to index over a shimano spaced 10spd cassette. Who doesn't want a campy equipped "vintage" mtb with a 2x10 or 1x10 drivetrain