Rare twin that shares many cycle parts with the 500 single and runs quite well if in a rather mild and constipated manner. Later engines have tougher internals but spares are rare and all manner of bodging may’ve taken place. Best to find a 1956/59 stocker. It should be smoother than an A7 or T100; a lot of poorly assembled motors pump out oil. If you find one with a spare engine or two thrown in, worth buying as relatively cheap.
1948-59 499cc OHV twin, 25hp, 95mph, 60mpg, 420lbs