I would expect the gun to be marked 2 3/4" on the barrels themselves, not the flats. Recently traded for a late 16ga Sterlingworth (39-40 vintage by SN) and that's where it was marked. On the other hand, my 1927 vintage Ithaca NID (with 2 3/4" chambers) has no marks at all on the barrels, where I would expect to find the 2 3/4". Probably because the barrels have been reblued. Hoof, anything at all marked on the barrels of your Elsie? If not, especially given the other modifications it's undergone, I'd suggest that a reblue probably lost your original markings as well.