The big difference is in the bottom pads and bases. The fabric seat base has a sort of pan where the cushion rests, partially resting on the springs. The leather seat does not have this tray.
Also, the leather seat is completely attached to the base with plastic clips. The cloth seat has a couple of hog rings in the front and a couple on the sides, but it also has plastic clips all around.
Leather seat:
Fabric seats:
The mounting points for the plastic trim on the seat bases are also different, as are the shapes of the armrests on the armrests:
Because of the latter, I had to use the fairing from the leather seat, even though the mounting points didn’t work properly. The only thing that matched was the screw on the back. I had to use the zippers judiciously, and the fit still isn’t quite right – you can see some of the “structure” of the upholstery after wearing. I can make a better effort later.
But otherwise, with the original seat base, everything plugged in fine. The airbag light on the dash went off as usual. So I will declare this effort a qualified success.