Too much going on this weekend to spend more than a morning out in the garage, but I got a start on building the seat mounts. I'm starting with the right side so any mistakes won't matter as much. It's slow going in part because I'm making this up as I go along.
I'm starting out by getting myself a reasonably flat, level surface to work with
From here I'm thinking of using 2" channel to go from the base I just made to the bottom of the seat. That'll have the bottom of the seat about 3" off the floor. From sitting there on about 3" of lumber with my helmet on, it seems like a reasonable height.
Next weekend I can work both days, and I hope to complete both mounts.