Join VOC.
There seem to me to be two markets: collectors who imagine that all Vincents were like peas in a pod and were "standard Vincents". Such people are not interested in whether or not it would be a money-pit if ridden, because they don't plan to ride them. They're interested in whether or not it has what they believe are "the correct parts". This amuses me, because MY Shadow left the factory with a "non-standard" black-painted front wheel, and "non-standard" black-enamelled STEEL mudguards. My! Who would have thought that THE FACTORY would produce a non-standard Vincent? Apart from those who know they did when the need arose. No shortage of Rapides around with Shadow clocks fitted because the factory were temporarily short of "standard" 3" clocks...
And there are people who want to ride them, who are aware that the odd paint-chip or non-standard item won't leave them stranded by the roadside, but a crank on its last legs, or a timing chest built by a moron, will. And who know that if the bike has been in regular use, it is less likely to be on the point of collapse. And who are interested in sorted bikes that can be taken beyond walking distance of the house. The second lot are mostly (but not exclusively) in VOC. And if you are that sort of guy, and if I were selling MY Shadow (which I'm not) then I might favour your offer over one from one of the w*nkers aforementioned. Joining VOC tilts the odds in your favour...it's a well trodden road.
(This post may have simplified matters in the interests of heightening the dramatic aspects of finding a Shadow (or whatever) and buying it. And not then discovering that you've bought a money pit.)
Note that I have not mentioned JMR anywhere in this posting.