Looks like you have a bronze/brass plate Virginia lock from Chambers (the mainspring gives it away). First, I'm sure Chambers would swap with you no questions asked, so maybe give them a call.
With that said, with that lock or the small queen anne, I prefer to deepen the pan there anyway. It gives a little more flexibility with the touch hole location. If you don't want to deepen it, a high temp silver braze will fill the void nicely. I used a brass color braze to fill some voids on the French pistol guard and they're more or less invisible now. The repairs tarnished a little darker actually.
-Eric