Weird - no 1980 R90/6 were produced - ended in 1976. Frame number seems to indicate it is an R80TIC 04/79.
Made 04/79. I'd say "R80TIC frame 04/79" and maybe add it's historic reg compliant?
Thanks - my memory is just not what it was - I have a load of old airhead stuff which I have just got out a friends barn - including three engines and I thought that I had three frames - but maybe 2 were thrown away during the period when we lived in France as they would have just looked like very old "bits of metal" - motor bike frames - I'm sure one was a 90/6 ..... but maybe not

I have a load of old airhead stuff which I have just got out a friends barn - including three engines
Engines you say.
I may have need of an engine
Not far at allThey are really heavy - how far from Winchester, Hampshire are you?