There's not much to it. I just cut some 1/2 ply the size of the seat bottom and attached it with the bolts that once held the tracks on. From there it's just fit up and finish out how you like. One thing to know, the pedestal post should be set right under your butt - if you get it too far forward it'll pitch you like a jittery colt.
I was just curious if you'd used wood or fabbed something out of steel.