At least I had some outstanding luck with my 1st 500 (in my avitar),- back in 2005, I found it advertised in the local paper for $1600 - it turned out to be a 3 owners from new, nearly completely original bike, for which I payed the nice gentleman $1400. A bargain I think as a few weeks later I was offered $3500 for it - I seriously doubt I will ever sell it though!!
My 2nd 500 my next door neighbour lined up for me back in 2007 - he knew a guy that had one which he'd started parting out but then decided he didn't want to get stuck with it - I scored it for $200 but with all the missing parts now replaced, a new paint job done on the tank & covers and the carbs rebuilt, I am quite sure it owes me far more money than my 1st one!
I think I'd have had a lot more trouble with this project if I didn't have 2 cb500 fours to use for reference, diagnosis(by switching parts back and forth), and to borrow parts off while waiting for the latest ebay part to arrive. I have been very careful along the way not to lose track of which part originally belonged to which bike and as soon as possible I always return the part(s) to the bike they belong to. (Well nearly always - I have muddled up some of the rear brake parts and the headlight buckets for example and have no way of knowing which bike they originally belonged to - they don't really matter to me, but I am more careful since then!)