Well it turns out I lied. A few weeks ago at a gun show a guy was Giving away old MUZZLE BLAST magazines and I picked out a few. One was from Jan 1984 and as I was taking my morning "read" (sounds better than dump) I leafed thru it. Lo and Behold! there is an ad for your gun. Midway Arms Inc had bought up the last of them and was selling them for $295! The following is based on the Photo in the ad and pictures in Bairds HAWKEN RIFLES.
I can't tell what finish your gun has but it should be rubbed oil, not the glossy type that Browning often uses.
The furniture should all be browned steel. (Trappers didn't want any bright things).
The JBMR lock is quite different so the wood around it is also has a different shape. Almost all the Hawkens seemed to have lockplates similar to the average lock shape (like a new Sylar lock). The gun in the ad has a larger much more rounded shape forward of the hammer.
The JBMR Trigger guard is similar but is more rounded. The Hawken guard is much more elliptical.
The rear of the guard looks authentic but I can't tell how it's attached. The Hawken used a screw from inside the trigger plate into the guard. The front had a stud which was screwed into the trigger plate ahead of the triggers.
I can't tell what your trigger plate looks like but the original Hawken plate was 10 inches or more long and extended from ahead of the trigger guard to the rear going completly under the stock wrist. Some Hawkens (but not all) had a screw down thru the stock at the back of the wrist (or in the comb) into the rear of the trigger plate to add strength to this weakest place in the stock.
The shape of butt plate looks correct. (Some had more, some less curve).
The JBMR Sights are taller. This is typical of all newer guns. Often the originals front sight only stuck up 1/8 or less. I can't tell what the JBMR rear sight type is but both flat top and Buckhorns were used on the originals. They were of course non adjustable.
The JBMR general stock shape is very similar except the nose in the ad looks to be bright. It should be brown iron.
The biggest difference I see is the amount of drop.
I measured the add photo and calculated the drop as being about 2.7 inches with a 14 inch pull. Using the same method, the Kit Carson gun drop is about 3.14 if the pull was 13.5 inches (he was a little man), and another original was 3.25 based on a 14 inch pull.
Most modern Black Powder guns fail to use the amount of drop the old guns had. I'm not sure why this is true but I think it's because they think it will sell better to modern shooters and the stock designer has never shot a BP gun so they think the recoil will be excessive. (As you know, the "kick" is much softer with BP for a equal amount of muzzle energy).
I hope this helps you out, and remember these are just my opnions (which is what you asked for).