Attex produced two versions of the ST400R. The most common used a 6000 Baker/Hill transmission and the later one a T20. If it's the later model, it's worth restoring- not a common machine at all. If you look through the pics on the ATV racing section of the gallery, you can get all kinds of ideas for the cage, drive train, body, or whatever. Good Luck!
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far