OK, the good news is that I purchased a new O Silver 2 shifter and mount from eBay a week before they restocked then sold out. The bad news is that the seller sent me an O shifter with an X mount. The message from the seller was a shrug and a "that's what Rivendell sent me." So I have an extra X mount to trade if you need it. If you bought a shifter set from Rivendell, maybe double check that you have a matching mount.
I really do like the inside mounting technique for these shifters. They're easy to use and work well with pogies in the winter.