Thanks for those pictures.
The 1973 ones are slightly after my time and none of those serials appear in my log book. They look as if they are in grey/dayglo rather than silver/dayglo and they certainly have a later style of Squadron markings.
I attach my photo of WK548 which, frustratingly, does not show the aircraft letter. I seem to recall the letters were on the nose cowl only.
The picture is poor quality because it is a scanned hard copy - taken by me on a very amateur 35mm camera from another Chippy somewhere near Newton.