Check this out:
https://www.brattons.com/seat-adjust...-assembly.html
There is also a big spring that pulls the seat forward, you push against it with your legs to move the seat back.
Ratchet assembly mounts to floor with 4 flat head screws (if I recall correctly, they are 1/4"-20).
You can mount it with only 2 screws in the front holes, going into the rear mounting points, if you want, and move the entire seat back about 4 inches for added legroom.