This picture brings back a few memories for me as the fleet this truck belonged to would visit the farm I grew up on everyday to collect the milk. It belonged to Bay Milk Products based in Edgecumbe, Bay of Plenty, New Zealand. The Rb was indeed a New Zealand only model produced in 1989 as an update of the R-series before the CH came out. They were built in Palmerston North by Motor Truck Distributors using a local bonnet that featured an Ultra-liner grille. Incidently Motor Truck Distributors also built the very last Ultra-liner in the world in 1999 which conicided with the production line closure in New Zealand. I think they generally had a 350 hp engine and 12 speed mack gearbox, and the one in the picture is pulling a standard for the time "a-train" trailer set.
