Strikes me you have gone to a lot of trouble Chris to make sure about the true provenance of this weight. I'm sure everybody appreciates this, even if there is little or no acknowlegement.
I also know the seller of the other weight that was specially commissioned, I have bought many pieces of Selkirk glass from him and found him to be a gentleman in every sense of the word.
Personally, I would not sell this weight without putting a very good realistic start price that won't hurt if it doesn't go higher. In fact, in view of the special nature of it, should you be selling it al all?
I don't collect paperweights, but I do have a Colin Terris Designed one called Millennium Vision, a limited edition made in 1999. given to me by my Sister. I wouldn't part with it for the world.