I own two Nanni engine
and while you have a good supplier in the UK I have found Nanni parts
to be very expensive and Nanni to often be unwilling to help source something directly when they don’t have it in stock at the factory.
Nanni also has not made it easy to receive shipped parts
by refusing to drop ship and insisting they be routed through a dealer even though it would have considerable time money
to ship directly to the customer.
I therefore would look very hard at alternatives especially those which use engine
blocks made by other companies such as Kabota which might allow you an alternative route
for parts. Nanni does use Kabota of course but they definitely don’t make it easy to find alternative sources for non Kabota parts.
For sail drives I would shy away from ZF for similar reasons plus their own statements on the expected life of their drives. ZF makes drives for other engine manufacturers so check where they get their drives.
Nanni btw dropped ZF for at least some there engines. They went with Technodrive by Twin Disc.