Free is good!
Mike's right: that's a Baker-Hill, probably a model 7000 (machine looks like an ST300D).
That's an early Attex, first generation. The discs on the transmission are are for drive and brake: the inners stop to put power to the wheels and the outers stop the machine. There are planetary gears in between the two discs and a dual-action caliper on the base to achieve this. If I remember right, the engine is on slotted holes in the frame to adjust the belts. I like the cool pivot for the shifter; it will make removing the floor pan a little harder, but I bet it shifts better.
Good luck with the project!
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