Any mv restored to original spec is perfectly safe. The idea that you have to replace fuel lines and wiring with modern materials is rubbish. In some cases, modern is worse. A good example would be wiring in a tank engine bay. Modern pvc covered wire will not stand up to the heat very well and you'll end up with shorts. (in the wiring, not you!)
It is much more important to do the job correctly with proper fittings and ensuring cables and pipes are properly supported and fixed, be they original style or modern.
Certainly, original, i.e. 60 year old wiring can be a problem but age affects everything, isn't that right Degsy?
Edit. Gordons post reminds me that very modern fuel, especially if it has ethanol, seems to eat most traditional materials including brass but that is a fault of the fuel, not the vehicle!