In a roundabout way, we owe the existence of the Harley-Davidson XR-750 to the Brits. They didn’t design it or built it of course, but what they did do was complain – loudly and often – about the rules governing the Grand National Championship which excluded them (by design).
Prior to 1969 the American Motorcyclist Association (AMA) rules for the AMA Grand National Championship were deliberately structured to favor side-valve engines rather than overhead-valve engines.
The result of this was to favor American made bikes such as those from Harley-Davidson with their side-valve engines, and to disadvantage the overseas competition which was mainly from British motorcycles especially Triumph, BSA, and Norton. The AMA rules prior to 1969 allowed side-valve engines of up to 750cc capacity but OHV engines were limited to 500cc. With their 50% engine size advantage the odds were stacked in the favor of the side-valve bikes.