I think this may well be at Southbridge, Canterbury, in 1957, where there were 2 race meetings held, in June and December on a fairly rustic 4-mile-odd road circuit with about 1 mile unsealed surface! Probably December I think, the last "road" race held in NZ as distinct from "street" races (round the houses).
Where's his band of helpers, no-one to lug wheels around for him?
Stu