(Where were you when I was buying the drinks at Founder's' Day?)The Lucas unit is actually very sophisticated in that it controls the voltage going into the battery - both preventing draining the battery at low revs and preventing overcharging at high revs. It also limits the charge current to stop a low battery drawing so many charging amps that it damages the plates.
Adjustment usually justs involves keeping everything clean and dry, but when adjustment is needed, best to do it yourself, as there aren't any Lucas Depots any more. Some old agri places still have someone working on pre-alternator electrics.
I've directed a few people to this site for guidance: