These seat brackets are designed to be used to either mount directly to seat for a solid seat-to-floor mount, or can be used with the adjustable seat tracks mounted to the sides of the seat (that I believe David Borden pioneered?)  You will need 4 brackets per seat, so one set is good for mounting one seat.  Made from 1/8″ thick steel, they will require primer and paint before installation.  No holes are drilled into the base, as I usually place the brackets on the seat, and then figure out where the base of the brackets intersects the frame tube at the front of the seat, and drill the base mounting holes to line up with the chassis tube locations.  Slots in the vertical portion of the brackets is 3/8″ wide.