Cars were registered in those days as E Class A ,which was basically a farm registration for tractors etc to use the public roads.A lot of hillclimbs and race meetings,[like Waimate and Renwick],were on public roads so had to carry a plate and be E Class A registered to cover them for liability .
Few years back looked at a BMW 2002 for sale in Tauranga and the guy had it registered E Class A,never been picked up,dont know what would have happened if he had an accident and made a claim!!