After checking online and thinking again more carefully I've concluded the bike I rode was an 82 RD like the one in the photo below, but it was sold new late 83 as a clear out sale (NZ used to be the clearing house for old models) and I rode it 84.

I had an 81 YZ250 for a while and that had a lot more punch, but only for the blink of an eye, and it also handled like a bus and had horrible brakes. I'm sure the RD was much better but I had no idea how to ride a road bike.

PS - that one has RZ stickers but it was an RD that looked identical to that photo