I think the military reg was either XR807 or XR809, certainly one of the XR's.
I too love the VC10. I flew on them a lot as an Air Cadet based at Bampton/Brize Norton, sometimes three times a week in the summer holidays.... sad but true.
My last VC10 flight was by BA from Cairo in 1980. It is a pity they were not re-engined with RB211's but at the time Twin Engine Ops over the pond was not allowed.