[T5owner]

Acc. to the Mustang Production Guide (Jim Smart/Jim Haskell) pre-production cars got 5S1xxxxxx stampings. I will post later a pic of Alan Manns preproduction Mustang that he had as early as February/first few days of March* 1964 acc. to his mechanic John Grant and Alan. The car is said to be still in the UK and has a rather lower stamping in the first 10 digits of those mystery preproduction 5S codes.