By the 1960s the converted World War II-vintage types that comprised a large part of the Australian agricultural aircraft fleet were in need of replacement.
[1] Sasin Aircraft Service of Goulburn, an operator of a de Havilland Tiger Moth modified for use as an agricultural aircraft,[2] decided to convert de Havilland Canada DHC-1 Chipmunks for agricultural use and contracted Aerostructures at Bankstown to perform the necessary modifications.
[4] Aerostructures proposed a more capable version with a 110-gallon (500 L) hopper, MTOW of 2,800 lb (1,270 kg), and a 210 hp Continental IO-360 engine.
[2] A larger aircraft with four seats and a one-ton hopper was also proposed; in the event neither design left the drawing board.
[2] Aerostructures also performed a two-seat non-agricultural conversion called the Sundowner that had many of the same modifications as the Spraymaster, and which had wingtip fuel tanks as well.