It's like a Mowery rifle: http://www.gunbroker.com/Auction/ViewItem.aspx?Item=163561086 and there were 2 different Wesson rifle replicas in the early '70s that were similar. I have Mowerys in 40 and 58 cal, the former is a light gun for small game and the latter is a pig and appreciated for that!
I remenber a replica Allen cased rifle. It had a very short barrel and a detachable butt stock. The design honored a "Sunday After Church" shooting kit from the 1820's.
Sorry for the detour, but the weight/handling is mostly in the barrel: length, caliber, profile. It is simple to build, very few parts. Matching barrel threads to the action would be the biggest hump.
Regards,
Wiley