I haven't had COFFEE yet, but I'll try:
They're replacement Bar Stool Seats, mounted on 3/4" plywood panels. Under them are swivel mounts I found @ Bass Pro Shop & they fit the built-in seat nuts perfectly. Bottom panel has a piano hinge, at the front, mounting it to the seat riser, allowing the seats & panel to open up to the tool storage area. Gregg, (RIP) mounted an adjustable length bicycle kick stand under it, to hold it open.
They gave me QUITE a lot of extra leg room & I sit about 3 or 4" lower.
Also gave a lot more room to get your feet in past the "A" post, as it doesn't hang over the seat riser, like the wood spring platform did.
NO BODY mods & can be changed back to stock seating in about 10 minutes.
To get more room to get his feet in, with stock seats, one Guy cut off about 4 or 5" from the front of his seat platform & his springs. (Of course, that DIDN'T give him more LEG ROOM.)
Bill W.