After several years of looking I finally found the bike I've been looking for, a '79 XT500. I was a bit nervous because it was on eBay and I had no experience of that 'size' of a purchase. As things turned out everything went smoothly: the seller was easy to deal with despite being halfway across the country; he did a great job of crating the bike (using enough lumber to enable me to build both a bike stand/work table and a work bench); it arrived intact and started straight away. Like Sophie, Gromit (as the XT is now known) is a '10 foot' specimen. Looks great from 10 feet, but when you get closer you see all the warts a 30,000km, 28 year old bike picks up over its life.
I've put about 1,000km on it, including one moderately gnarly trail ride. Was it worth the (probably) high price? Hmmmmm...that's a toughie. Ask me after a winter of fettling! So far Sophie has not sulked at all.