Just a couple photos of the bare solo seat pan I built. You can't really see it in the photos, but the rear of the seat has a "flare" to help give the seat some shape. Took it to the upholster today. He'll get some foam glued on it and sculpted (hopefully) to my liking. If all is good at that point he'll sew up a cover.
The bumpers on the bottom are plastic, but I'm going to keep my eyes open for some rubber, "cushy" ones of the same height. The one large pin on the bottom engages with the stock seat latch. The other large one will fit into a large hole on the right, where I'll put a rubber grommet to keep it from moving around, and the tang on the front will fit under the head of a 5MM screw that I put into a hole that was already in the frame's backbone tube. The pan is contoured to seal against the tool tray weatherstrip. It's not the prettiest thing I've ever built, but once it's covered who's gonna see it?
Should get the "pad added" version back next week to have a test sit. If everything's OK the cover will go on.