If the bike is a collectors item you should be able to get quite a bit of money for it, it sounds like it's in pretty good shape and like it's as good as original.
I've got a 1974 Honda SS50. I invested over $2000 in it to completely restore the bike to it's former glory but because there are quite a lot of them around where I live I wouldn't get much more than $1000 for it. If I had a Honda ZB50 in the same condition I could get nearly $3000 for it, while this bike has the same engine as the SS50. It's really a question of what is in demand.