But that was not it. The new seat is as good as finished, only missing attaching a couple of straps that will work to stretch the leather around the seat. The new seat leaves some space between itself and the frame. So we made a little bag that'll attach to the underside of the seat and that fills the newly created space.
The seat nucleus was made of a piece of scrap wood that we had lying around, with some scrap metal from the junk yard wrapped around it. Tools used? Hammer. Canvas and leather for the saddle and canvas for the bag.