The seat pan was an option for the X-6 / T20 250cc Suzuki Hustlers in the very late '60's. It came upholstered, in a diamond pattern seat cover (if I remember things correctly from 40+ years ago LOL!). There was a matching (fiberglass?) tank as well.
Looked pretty trick for the time. I never saw one on the street in my area (Hamilton, ON. Canada) but I gather you could buy new X-6 from a dealer with the parts already installed. As far as I know, it was available as a kit so you could retrofit your bike and you could possibly buy the parts individually from a Suzuki dealer, too.
If I go down into the store room and look around at some old magazines, I might be able to find an article by a guy named Carl Caiati, who put the seat and tank on a CB450...
Enjoy the '60's.
Pat