BSA made 3 different versions of the B50 – you can probably guess what the B50MX was for. It was offered starting in 1971 for off-road competition, but within a couple of years BSA was dead and some remaining stock was sold off as the Triumph TR5MX. Expect 34 horsepower out of the out of the 499cc single, to motivate 240 pounds of bike. For more on the B50 line, check out this buying guide from Sump Publishing.
This bike (VIN: BH00482) is said to be “100% Original including Tires, seat, grips, fenders, exhaust and spark plug” with just 10 hours of use! The seller says that it’s still on the original MSO (included in sale) as it has never been titled. The sale also includes “all the books and manuals.”
Find this BSA for sale in Wilsonville, Oregon for $6,995 here on Craigslist.