Disc brake top nut and tube sleeve
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
Thanks to Paul Linn for providing me with these photos and measurements. The top cap nut is part number MG# 13504541. The tube sleeve is part number MG# 13504441.
Ralf Brinkmann sent me links to some parts that Dieter Nelson had made by Holger Lauer (in Germany). Here is Dieter's information and the excellent machinist work by Holger Lauer. Ralf suspects the smaller fork top nut can by made by modifying the center bolt of the 650 cc URAL flywheel (URAL part number 90407).