Ryan,
I have a New Model Army with mixed serial numbers (barrel 91870 and frame 111955) and I know of another with a barrel number 91727 and frame 111547. In my humble opinion all three of these revolvers were shipped from the factory with mixed serial numbers. In my conversations with the late Don Ware, a Remington authority on Army and Navy Revolvers, I broached the subject of mixed serial numbers. His research led him to believe the Remington Factory did not let any material go to waste and as such would have salvaged good parts from previously rejected arms. BH was the cartouche of Benjamin Hannis a principle sub-inspector who inspected Remington Revolvers.
I hope this helps,
Bill