Lefever was in partnership with Barber in 1874-1876 & then with John Nichols in 1876-1879. "Uncle" Dan's patent for the side-cocker was #229,4259 issued June 29, 1880, or after he had parted ways with Nichols.
The hypothesis of it being a prototype & an extremely early Cocking Rod gun is for certain a great possibility, but I would think more likely made on a Nichols & Lefever frame than an L Barber one.
Most of the L Barber guns were in the 5K serial number range with the Nichols & Lefever guns being in the 6K range.
Whatever it is for sure a gun to be treasured.
