Once again from the Stein-Dinse catalogue:
https://www.stein-dinse.biz/etkataloge/etkataloge.php?l=de&h=MG&m=220&t=5368
#4 on the diagram, GU 95021114. The part offered for sale is apparently after-market, not original Guzzi.
https://www.stein-dinse.com/de/zahnscheibe-nml/item-2-1310507-95021114-.html
#8 GU 91120620, "spacer washer". This is an apparently original Guzzi replacement for GU 95005320
https://www.stein-dinse.com/de/distanzscheibe/item-2-1302017-91120620-.html
No dimensions there either, unfortunately.
The outside diameter could be guessed from the photo, I reckon. The thickness, perhaps more critical when they call it a "spacer washer", might be harder. Going by the picture, I'd guess something like 4mm.