Very well could be the chambers are original (2 5/8") as the measuring tool meets resistance at that depth. Could be a slight taper in the last 3/8" or so. At any rate I have no plans to grind metal out.
My last experience with a chamber length mystery involved a european 12 double offered by a very well known dealer, who reported that the chambers measured 2 7/8", although 75mm was stamped on the flat. In actuality the chambers were tapered in the last 1" so that his tool stopped 1/8" ahead of the forcing cones.
