Hi Peter, welcome to the Forum.
As your probably aware written material covering the period after the Great War until 1939 is pretty scant. The regimental book "Red Dragon" really skips over this period. I'm led to believe that eventually a Regimental Record covering 1919-1945 will be produced. So the diary will probably be of great interest. Are you intending to make the diary available in the future?
Bearing in mind the large number of query's we deal with on this site, we would be very interested in seeing the Drums nominal roll for that period, as its another source of individual detail, the sharing of this type of info makes a real difference. Its also possible that some info from the Great War may emerge. Which might give you some background to the boys he was serving with.
In the meantime, I have found a picture of guys your father would have known, taken in the 1950's, at least one of them is listed as a Drummer
[tmb]ftp://u37768419:fusilier@ftp.rwf-forum.co.uk/misc_pix/Oldcomradesre-union1953.jpg[/tmb]