people really wanting a Vincent have a few choice these days:
buying a real, expensive, one
building one from scratch, all the parts are available news
do as I did and opt for a "replica" of a Engli-Vincent as made by Godet or by another in the UK (name better forgotten!)
Can't say I am happy with my Godet: too many problems, dealing with a French is not easy (even if youi are French, like me!), in one word not worth the money I spent 5 years ago and certainly not the price today. The only excuse is the snobery piece of equipment, rare and expensive. I mostly love riding motorcycles and this can be achieved with better results on any modern cheaper bike! Like checking the time on a Rolex or a Kelton: its the same time!
Philippe