The problem with the dial bore gauges is that they don't have the reach required to do the housing bore on the mains except for the front and rear. Doing the rods and cylinders is OK as far as reach goes. You might get lucky and find some old Sunnen setup fixtures and dial bore gauges for the mains on eBay from time to time. Mics of all sizes and brands are on there all the time, so they aren't hard to find at all.
