I looked long and hard to no avail to get the 12" trapper version of the marlin 45-70...so I ended up buying the 1895 GS. I talked to a gunsmith about the same thing and he explained to me that he has to make a custom 12" barrel to make it legal ...to cut a factory barrel is not legal..
He quoted me for a custom 12" barrel installed, remount front sight ramp, threaded for a brake/redirector, crowned...and cut mag tube back -1 and re-dovetailed.....650.00 blued,750.00 stainless.
And it will be perfectly legal and non restricted.......the work will be getting done in short order...