There were only 3 different model '21's the r,se and sp and as you rightly say thats an r
And it's a bit steep for a tatty '21r in the current climate, they're fetching very low prices right now. I don't know if Jamie has sold his Pentax '21sp yet but it's complete, runs, is an SP (dry clutch, adjustable suspension and fancy light Magtec wheels etc.)
See the ad in classified here. The £500 more he wants for it is in the value of the wheels and suspension alone easily.
You might not care now but having "just" an R model will start to annoy you in the end.
I bet this 21se on Ebay doesn't reach £1100.
But '28s fetch considerably more money than '21s, if you can raise some more try your luck with an offer on this.
Also be aware; derestict a 21, nearly free - derestrict a '28, nearly a grand
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Please do not PM me technical questions, if you can't find it on the Forum start a thread