Actually when Shiloh and C Sharps worked out of the same building way back when they offered a "rocky mountain" rifle with that same Hawken type butt plate.
Neither the 45-120 nor the 50 140 was anything a person would use to shoot more than a handful of rounds at a time..
Leaving it as the Gemmer conversion and having it rebarreled to 44-77 would be a good use for that thing. Use the other 2 barrels for tomato stakes.