Frank..I have a brand new boxed ducati single seat for the later ie ..ive seen one fitted to your style of SS..think you just need the different rear light.
Anyway if thats no good, and you go for this seat or similar, ive got some (brand new still in the packet) OE ducati superlight white number boards with the number '1' and 'ducati campione del mondo' stickers.
Let me know if your interested mate.
nat