You are right Rich, 2" is about the minumum transom thickness. just a shade under is ok because there are washers under the nuts, and the inner mount is 1/2 thick, I'm not Sure about the MR's, but the studs in the Alpha assy's have 2 1/2 from the threads to the gimbal housing, the transom on my boat came out just shy of 2 1/2 inches, and enough threads on the studs to go through the nuts with washers.
Good work Tom