The L&R "Queen Anne" round faced lock works WONDERFULLY....with Siler internals!
I think that L&R tumblers and sears are just not sufficiently hard as they come. Which I could fix, but what I really don't like about L&R locks is that they just aren't "fitted" at all. The hole is bored in the plate at a standard size, and the tumbler is simply set in place, as it is cast to "finished" dimensions. They don't turn them down to fit the hole AT ALL, so unless I buy an "as-cast" plate (which they seem to be happy to sell to you, and I have done a few this way), there's no way I can fit a tumbler to a plate or bridle properly, as they don't give me any extra metal to work with.
I also don't like those miniscule little flys (or is it "flies"....).
I haven't fooled with a "Manton" in a while (got tired of it!). It will make into a very pretty little lock, but it does certainly have problems. One of which is the frizzen bouncing back and whacking into the top jaw, leaving a crease in it.
I think the Chambers "Late Ketland" lock might suit pretty well. It's kinda smallish, so I don't know how well it will fit on your design, but the Manton is small too.
Davis makes the rather larger "Twigg" lock. You know, I don't know if I've ever seen anyone actually use this lock. I looked at one at Tip Curtis' one time, and was quite impressed with it.