Well it's Harley derived so to speak. Buell unique pistons and heads and intake and exhaust. Valves and springs I think are uniquely Buell too. They are not just Sportster engines dropped into XB frames.thunderstorm is harely
On the books yes, technically no since they were not shared. Ferrari and Maserati are owned by Fiat but I would not call a Ferrari a Fiat.Well, Harley owns Buell, so anything developed by Buell is still a Harley product.