Tony P-J
If I am not mistaken, I believe that Master Technicians wore the same badge of rank as Master Aircrew, but without the 'golden eagle' in the centre. (I saw one once back in 1958!)
I think that you saw a Master Aircrew in a Greatcoat in 1958; the 'Brass' eagle can not be pushed trough the material of the coat. To the same end Flight Sergeants have cloth crowns on Greatcoats.
P G Hering's Customs and Traditions of the Royal Air Force (Gale and Polden 1961) has the Master Technician with a standard 'Tate and Lyle'
Regards CK