[MattKing]

Reid, my 180mm lens has both of those pins, mounted just like you said, behind the nameplate and slightly to the right. Their length (that protrudes) doesn't differ by much. The longer one is 8mm while the shorter is 7mm.

Re: parallax correction, yes..but shouldn't that compensation also be visible in the ground glass across the film plane? When I test the focusing accuracy of my 90mm lens, and when I gradually shift focus from infinity to the nearest distance (3.5ft), I can see the view on the ground glass gradually constricting and shifting a bit to the right, as per the shifting framelines in the viewfinder.

Now, with the 180mm lens, this doesn't happen at all when I rack the focus from infinity to 12ft. Strange, because I was expecting a telephoto lens like the 180mm to have an even more pronounced parallax compensation that will be visible in the viewfinder.

If the image on the ground glass thrown by the 90mm lens shifts to the right as you focus, then the focussing mechanism requires repair.

The shifting framelines are there to help match the view through the viewfinder to the view seen by the lens, which is of course not in the same location as the viewfinder.