Yeah, a very nice little lock!
Seems to me that you could add a little mild steel to extend the bolster if you want. A little brazing with a fine tip on a MAPP gas torch would do the trick.
Here's a photo of your lock as compared to a Beckwith, London, ca 1810. The arcs I drew in show the approximate swing of the tumbler arms. The back end of the Beckwith bolster has been filed so as to give the maximum amount of room for the lock bolt. The bolster on yours is a bit shorter than need be on the bottom side.
You might also want to deepen the pan a bit.
Anyway, I'm just chatting here...
Here's another view of the Beckwith, without my distracting lines...
Beckwith, London- 14-Bore Single Barrel Sporting Gun ca. 1810
(original photo of the Beckwith was from:
http://www.drake.net/products/Beckwith-London--14-Bore-Single-Barrel-Sporting-Gun-ca.-1810?id=28546 )