George, welcome to the world of the L.C. Smith. For what I know "elsies" in 12 ga . were always manufactured with 2 3/4" chambers. As for the cracks behind the sideplates, probably from using high velocity loads, or some screws loose. David Trevallion is probably one of the best stock makers in the country, but what you need is to have someone acra glass the stock. Here on the forum our own Dr. Bill Hambidge does such a job and also highly recommended by Ken Hurst is Boone Berlin (910-220-3332). Also I would shoot low pressure loads under 8,000 psi. in any "elsie" or older gun. Hope you will join the L.C.S.C.A.