Nonetheless, if a handgun or other weapon with an overall length of less than 26 inches, or a barrel or barrels of less than 16 inches in length is assembled or otherwise produced from a weapon originally assembled or produced only as a rifle, such a weapon is a “weapon made from a rifle” as defined by 26 U.S.C. 5845(a)(4). Such a weapon would not be a “pistol” because the weapon was not originally designed, made, and intended to fire a projectile by one hand.
Sounds like, if your barrel is longer than 16", and the overall is longer than 26", you are ok...
I need to read that more thoroughly, since it addresses the T/C Contender issue... thank you for providing the link to it..