That is a really cool looking bike, and it looks to be amazingly original-- like, even the orginal bar tape. Personally, I don't think a vintage Campy makes any more sense than, say, Suntour. I'd get the Benelux system working as well as possible, and then find out if the bike is fun to ride. It may turn out to be a bike that you only want to ride once in a while, in which case it makes sense to keep it as the classic it is. On the other hand, if it turns out to be a bike you want to ride a lot, take the Benelux stuff off and store it, and put less valuable, and more functional, derailleurs.

Thanks for the Benelux manual, too! That may prove to be a valuable resource. In fact... do you think you do a better scan of it some time?