Nice! It looks original other than the tires so if it is untouched from when it was built in 85 you've got something. Personally I'd keep it and ride it once in a while but there's original R's for sale over $10k so I'm sure someone would pay that just to park it in a showroom or garage.
I think your best bet, if you are not sure, is to start high - post it all over the place - see what offers you are getting then come down to something more realistic. I think 6K is high, but you never know.