A Traditions Pa Rifle isn't really correct for the period either, but they don't look too bad. There is no rifle correct for "what the early mountain men would use back in the rev war era." The Mtn men era is usually considered to be Rocky Mtn fur trade or 1825 to 1840 or so as compared with 1775 to 1780. The guns produced during those times are quite different but many older guns were in use also so the rev war era gun would still be appropriate for the later period. People used what they had.
Custom and semi custom longrifles are quite expensive but can be had for about 30% less than the listed prices at Track of the Wolf. Track's markup in their consignment sales is significant. Tenn Valley Muzzloaders is a semi-custom shop with a product that is a good value. Still a lot more expensive than most modern rifles.
I don't find smoothbores to be particularly finickey as compared to rifles. Keep in mind that many are not equipped with a rear sight.
He can get pretty close to an early fur trade era mountain man with a PA rifle... Hugh Glass had one made by Angstadt in Berks County. It was apparently a nice enough gun that he tracked down Fitzgerald to get it back.
Even the Hawken as we know it today isn't really correct for the mountain men... The half stock came near the end of the Mtn Man era and is more correct for 1840's to 1850's era... Oregon Trail and westward expansion period.
A guy can get by with quite a bit iwith his persona if he does some careful research into the era he wants to portray.
Mike