Since it is cyl you can not go by how long the choke is. Even in 1875 is was not that odd to come across a gun with no chokes. Old shooters could order guns, to their personal desires, and many were happy shooting guns without chokes.
As to barrel length 29 3/4" is odd. Could have been a 30" gun which needed the barrel muzzle end cleaned up after minor damage or they could have been 31" or 32" and cut back to match later 30" norms. Might figure it out by adding weight to the muzzle and see if it balances on the hinge pin.
Smarter people than me should be able to calculate what a inch of barrel should weight. I'd figure three to four ounces to balance at the hinge pin would point to a 32" set of barrels. But does it matter? Changes made a hundred plus years ago are as much a part of the gun as they would be 130 years ago when first made. British shooters as not as obsessive about factory originality as we are. And you are what the fourth to enth care taker of this fine gun? Guard it well and make as few changes as possible to keep it running.
