Dave, I found the original seat covers recently (thought I'd thrown away). The pictures below may help with identifying a set of covers that more closely duplicate the originals.
As shown on the images, the major difference from original and the reproductions is the seat material is cut different. Stock has one piece you set on, with a separate skirt going down to the floor. Reproduction takes the seat part down to the floor. Saving a seam. Hadn't really noticed the difference till you pointed it out. Good Eye!
Sorta wish now I hadn't cut the originals off the frame. Maybe next time.
