I have it in my mind that I saw somewhere recently that 48-037 was one of them but I can't remember for the life of me where I saw it.
I saw one of them at Prestwick when I was a youngster (a diversion) and it definitely did not have an RAF or USAF serial number anywhere.
It is recorded in my spotter's log as "5856". Perhaps that was the radio callsign (as in Rafair 5856)?