I agree the Late Ketland could look a little dainty but if you build the rifle around the parts instead of following a precarve stock design, and rounded the tail, I bet it could look good. You might want to go a little more "Maryland" in style than "fully developed plains rifle" with that lock. I'd like to hear what Don Stith, Taylor S and Louie Parker would say about lock choices for flint Hawkens.
I sure wish there were more models available for the late flint period. I'm not a big fan of the L&R Manton completely waterproof pan. Otherwise it's a good looking lock for an American rifle of the late flint period. Just seems a little sophisticated and fancy to me. That being said, I used it for a flint Hawken as there was nothing else close back then.