Mike, I was at that match and still have the programme. Like you I can't remember whether John Charles played or not but as you say he was certainly down to play in the programme.
For the record the Millers scorers were Bob Williams (3), Galley (2) and Barry Lyons
High scoring games like this one were typical of the Jack Mansell era. He was appointed just before the 65/66 season started and we finished 7th. I was at the Birmingham home match ghat December when we were 3-0 up at half time and lost 4-3