Those men in the white overalls at Paya Lebar were Qantas ground engineers.
I was one of them until 1966 when I joined Cathay Pacific as a flight engineer in Hong Kong. I had three consequtive postings to Singapore which were the happiest six years of my life, not to be forgotten. Qantas engineering had a virtual monopoly on the handling and maintenace of most movements of Brittanias, Super Constellations, Lockheed Electras, Convair 880s, B707s, Comets, VC10s and all ods and sods of charter flights, delivery flights, etc.