I think I may have answered my own question by translating some of the Italian on a diagram of the relay & dynastart wiring.
The suggestion is that if you want to use a dynastart with the standard regulator for the Militare version, you need a relay. The Lucas SRB 325 was specified.
The regulator for the Civile already has "protection" or is already suitably rated to not need a relay.
I had to search round various posts regarding the pulley. Modern pulleys are available with suitable taper lock bushes so that mounting on different spindles is not a problem. I can source this and the shorter drive belt quite cheaply.
It looks like I'm going to be busy!