Why not?
Seriously, I have a couple of barrels from T/C; a .54 that is 9" long and a .50 that is 12" long. They are part of an interchangeable barrel setup I have for my "Yellow Bird Gun", which is basically a New Englander walnut stock with a Greyhawk lock and hardware. These barrels are 1:48 and stabilize round balls just fine.
My T/C Patriot pistols also have a 1:48 twist, and are quite accurate. Other pistols of that approximate caliber vary from 1:18 and 1:24, but those are generally revolvers. That is too fast for a patched round ball as the patch will probably shred even with a light load.
1:48 is a "compromise" twist rate and will generally stabilize round balls and conicals fairly well, but ideally, you want slower twist rates in a round ball barrel and faster twist rates if you are going to shoot conicals or unmentionables.
I would guess, that if the barrel remnant has a 1:66 twist, that is what you will be using and it will probably stabilize round balls better than it will any kind of conical bullet. If it doesn't, then your only other option would be a re-bore to .50 caliber and change the twist rate to whatever you want.
T/C has always maintained that the twist rate is relatively unimportant and that different powder charges and other factors have more to do with accuracy than the twist rate. They are probably right, but I do not completely agree with this notion. I have guns that will not shoot PRB and others that will only shoot PRB accurately.
All that said, you probably need to hear from somebody who has actual experience with slow twist rates in muzzleloading pistols.
Good luck.