To PTK and others--problem solved. PTK, you might want to go back and read the letter in your own post--specifically the third image.
This is the part that says, "It is the position of ATF that if a multipurpose firearms kit is obtained as an assemblage of parts from a single source, the components of the kit can be assembled and re-assembled an unlimited number of times as a rifle or a pistol."
Moreover, I'm sure that you noted that the preponderance of the letter dealt with the Thompson/Center Contender.
No, I'm not a proponent of the Mech-Tech unit. I don't own one, and have no plans to buy one. Still, the answers are there--now posted in writing, and posted on this board.
And, I guess I'm done with this one. Bye, y'all.