Looking closely at the photos posted here, the only thing that would lead me to believe that this lock might have been flint originally is the chunk missing above the lock that might have been clearance for a flint cock stop. But it could also just be a chunk missing. Or, perhaps this entire lock is a replacement for a late flintlock that might have preceded it, and this replacement is a good fit? Tough to tell trying to zoom in on the photos on a laptop. I can see by the xray image that it looks like a 3-screw bridle and I can see a stirrup tumbler. *IF* this lock is a complete replacement, it's possible that the current lockplate is a little larger than the original. Real tough one here. The hook at the nose of the plate to eliminate the front bolt would be pretty standard for either a late flint or percussion.
Most of the time, when the lock companies or resellers (i.e. track, mbs etc) are specifying barrel size, they are going by the interaction between the bolster, barrel and mainspring and whether or not a given bolster thickness with allow the particular mainspring to clear the barrel. There are lots of alterations that can be done here. 1.25 breech in .56 cal still gives you a lot of meat there so if there are issues with the mainspring clearing, you can thin the spring, or file bevels onto it, or chisel out a bit of a barrel groove or all three.
I've used a couple of those Davis locks that were basically the HF lock without the markings, but I modified the heck out of them. Never had a problem with one, though. I'm generally not a Davis lock fan but did not have issues with them but to be honest I was replacing some parts as I was modifying. I'm not sure if the 'common rifle' or unmarked version is still identical to the HF lock, as I see they sell common rifle locks now that don't look exactly the same to me.
Edit: so I took at look at Track and they still show HF lock with engraving and without, but being the same lock. However, the unmarked lock is backordered. That may be in perpetuity *if* Davis is no longer making them in that form. One point, since it largely uses Siler internals, (1) replacement parts are piece of cake, and (2) the Siler mainspring can easily accommodate bevels filed on the arms, particularly the upper arm in this case, which will buy you at least 1/8 of barrel size or more depending upon how aggressively you file the bevels. It can be done without annealing or retempering the spring and it will have no effect on function. If you can still get one of these, based upon what you want to do, I would go with this lock but expect to do some fairly simple modifying (no welding should be involved - all cut and file).
