The 3 is on the reinforcing bar, no other numbers, a noticeable space, and then the capital "C". I figured the 3 referenced the grade as well, and I don't recall any unique markings on the barrel flats or the water table other than the serial numbers, but I'll pull her out tonight and take a look with my "cheaters" on and in good light.
I'll have to snap some pics and post. I figured someone would know about the ivory; guessing either the owner lost the dog's head medallion, cracked it, had it replaced as a unique marker for his gun or some combination thereof...it has obviously been in there a while.
Thanks again for the help. I am hoping the gunsmith says she is good to go with low-pressure loads...wondering how far away a dove wouldn't be safe with the x-full chokes...or a mallard or two...