XSP numbers Graham HILL (No, not the late great F1 driver but another) has…

XSP NUMBERS
GRAHAM HILL (No, not the late great F1 driver but another) has recently acquired some cross-flow heads which have interesting serial numbers stamped on. Would anybody have a record or knowledge of the markings? On another topic, he recently saw a Mini with an XSP number attributed to it which I find a bit suspect. XSP 4770C – any thoughts?
If you can assist with the above please let me know via feedback. Graham is also looking for detailed photos showing the injection system fitted to the cross-flow head on the ‘works’ cars.