Forgot to check this forum, so sorry about the delayed response.
My Mk. 2/1 is serial #21 and engraved O.S. 1650A., with no O.S. 1400GA. marking.
Agree and will keep it, but it would be nice to also get the matching scope, which I understand is a Houghton-Butcher Mk. 1, which I further understand is a PITA to adjust and requires that silly little tool.
Much appreciate your advice!!
BTW, I was able to get one of the last copies of your Telescope Sighting No. 32 book from Brian. Very useful info and glad to have it.