The gun does have a prefex before the number. I couldn't make it out after looking again I'm sure it's a 'B'.
The B prefix was for guns made for Gibbs partially or entirely by other gunmakers. Original proof marks are Birmingham, 1887 rule. So, with a B prefix number, this gun was almost certainly sourced from a trade maker in Brum. That's probably why the Henry is a ringer. They could easily have come from the same source.
Look on the fore-end loop or around it ( lower rib between the loop and the flats, bottom of the barrels, etc.) for a non-matching number. When the trade makers assigned their own serial number to a gun built for someone else (not all of them did so) this is usually where they put it.
