You want answers? Ask 100 Vincent owners, to get 200 answers. The B was superseded by the C with forks (Girdraulics) that Vincent thought were an improvement. Widespread opinion is that the B with Bramptons, handles better, which probably means "give more feedback". I have a C Shadow, which 1) was available to buy and 2) I thought was the definitive Vincent anyway. I too have many bikes, and I wouldn't choose the Vin for a "scratching round corners" competition, but that's not what I do with it. There's something about that big vee-twin turning over slow while the horizon gets closer fast that makes it a wonderful device. It is also a pleasure to ride in traffic, surprisingly nimble. By chance, mine does have matching numbers, but I know of a very good one that doesn't. A better motor became available, and was duly fitted. The result was a stunner. That was when people were more interested in bikes to ride than bikes as investment, but times change. I think you might find that a matching numbers B will cost a lot more than a matching numbers C, and neither may be better than a mongrel.
Best buys are probably bikes that are well used. They've been sorted. Something to bear in mind however is that a Vin leaving the factory would probably do 50,000 miles before it needed serious attention, so if you buy an old one, it might be at that stage. A purely personal opinion is that the road to ruin starts by buying a bike, then immediately stripping it for an overhaul. Like all bikes of that era, Vincents were selectively assembled (a Shadow is a Rapide blueprinted). They need to be selectively re-assembled. Not too many people can do that, and delivery times vary between a week (honestly) and three years. So if it runs, ride it for a year or so to find out what is needed.
More immediate advice is to invest in the literature. There is a lot of very good stuff on Vincents. Know Thy Beast (author Eddie Stevens died this year) is essential. Richardson is good. Forty Years On and Another Ten Years give a vivid insight into the waves of needless panic over oil, plugs, whatever, that sweep through the Vincent world until everyone relaxes. All of these can be bought through the club. And join the club. I was told many years before I bought my bike that it was worth it just for the magazine, and it was true.