I just received a large haul of archives as well as some misc motorcycle parts. There were a few number plates and i noticed two consecutive, but didn't think further.
Next day I found a large photo of an indonesian riders race bike with one of the plates bolted to the side of the fairing. What a memento.
So it's a 1973-4 plate with O rego, i've seen them a couple of years later with E rego.

who knows what these to classes were actually designated as please?