Rank and insignia for 6th AGRA

[Broadlee30]

Hi,
Researching my family military history and have his an annoying snag.

My Grandfather was a Staff Sergeant (75th Highland (heavy) Regiment RA) assigned to 6th Army Group Royal Artillery. He fought in North Africa, Sicily and Italy (casino) etc.
The story is being pieced together nicely but when it comes to his uniform, we have photographs but none really in his KD and cannot determine what insignia was worn and where, He does have 8th army shield and cross, and the greek letter M but as a staff sergeant how was this all presented ? was there reference to the 75th? Really am struggling with this.
I have acquired a replica KD top he wore, his ww1 campaign medals, dunkirk and the like and want tor replicate his uniform in honour of him.

can any one help, I will be going to Stoneleigh on 3rd Feb but would like some advise before if possible

Merry christmas

Ian