Hey Dave,
I haven't studied much in the way of late flintlock American guns, but lots of late English shotguns had lock panels that tapered widest at the front and narrow into the wrist. These also had cut away breech sections and fancy locks built for such things, not found on most American arms. Most precarved stocks I've seen have tons of extra wood around the lock panels, you may be able to lay in a lock and make parallel lock panels - if you can, I'd go for that option.