Hadn't seen this post before, but figured I would comment on it. They were pretty short lived, because the seat was "Towed" behind the power unit, you held on to a bar that had the throtal and brakes on it.
Problem is that when you went down into a ditch and the unit climbed out the other side, it tended to break both your Femor bones when the bar came down and the space between your knees and the bar disapeared.... Great on flat land though...
Cleats were easy to make though, Oak wooden strips....