The XR-750s DNA is from the Sportster. The original XR-750 was a de-stroked iron barreled Sportster that used magneto ignition. This ran much too hot in a racing situation and was replaced with an engine using aluminum heads and a more stable rocker assembly, but it was still a pushrod, roller bearing bottom end engine with four individual cams each on it's own gear, just like a Sportster, K series flathead and the earlier W series flatheads. The cam drive on Ws, Ks, Sportsters and XRs hasn't changed significantly since 1929. Keep in mind the Sportster started out as a flat head K with overhead valve heads. The same lifters that opened the valves of the K series flathead instead operated long pushrods to the rockers of the OHV Sportster, and the XR-750.
I live in a parallel universe but have a vacation home in reality.