Originally Posted by Parabola
Pre-1875 Proof marks are usually (as on Shrapnel’s gun) stamped on the tubes rather than the barrel flats.

Yes, the 'old' marks on mine (including the "JT") are on the barrels exactly as Shrapnel's. Unfortunately, my contact was unable to provide a name for either JT or JK. It is possible Steve Helsley may know, or know someone who does.