Used to, but not anymore. You used to have be in a set height group, etc, so that you all looked nice and tidy. I think they got wise to people putting in for a full set in about August, and those who suddenly needed glasses around the same time...
Sounds like a windup to me. I'm sure I heard this buzz when I was a young sailor, I wore specs when I was on shore patrol, and when taking part in Guards, and that was in the 60s/70s - but seriously, I do not think the Discrimination rules would allow anybody to be refused taking part in a ceremonial duty.
Did you know that for Winston Churchill's funeral, the gun carriage crew were mainly senior rates dressed in square rig. The majority were gunnery rates and GI's from Whale Island. Just a point of history.
No idea WM, never got to Pembroke. There is also one in the entrance of the SR's Mess in Viccy Barracks. I think that one is for King George and is pure silver, with a name plate for every rating on the carriage.