Late to the discussion, but IMO a fullstock Hawken and large bore smr are the same thing with different trigger guard and sideplate/escutcheon. And possibly a patchbox. The Hawken boys worked at Harpers Ferry where they knew the 1803 halfstock rifles, and they knew of the mtn rifles built in the hills all around them. That's probably what they built in St. Louis, and smr's went west with early mtn. men.
Johnson's Kentucky Rifles book pp. 178-180 has 3 examples by Duncan, BHC and Goss(Gross), .52, .55 and ?, though with longer barrels and probably a slight swamp. There are more out there, remember a couple in the Colorado Hist Soc collection. I put together many Sharon and other fullstock Hawken sets of parts, some as Hawken, some as smr and some hybrids. Folks liked them and the story. Build what you like, possibly make it look cut down from 46" barrel. Bob