Classic motorcycle

Been nearly 30 yrs. since I had a bike and I got the itch and probably enough money to buy a decent project bike. I know the newer bikes probably handle better but I can't help but prefer a good ole classic. The last bike I had was a 65 Triumph 650 that was mildly chopped that a buddy gave me for rebuilding his 318. I'd really like an Indian but no way do I have that much money. Same goes for a classic Harley. I really liked my Tr and wouldn't mind owning one again but I don't know how easy they are to find parts for?? Wondering if anyone here is into classic British bikes and could comment on that. I remember my Tr had British standard bolt and nut sizes that was a PITA. Do BSA and Norton's also use British standard fasteners? What would your choice be between those 3 and why?
Vincent Black Shadow. 69-72 Norton Commando Fastback, 1969-1971 Triumph flat tracker.