A Brief History of the Marque
George Cyril Stillwell and his father Walter began building motorcycles in Melbourne in late 1912, and these were branded as GCS. Components were mostly English, Swiss and American. When Walter retired in 1916 George took Leslie Parry as a partner - together they established Stillwell & Parry Ltd. Initially they built their own machines but by 1918 much of their stock was built by A.G. Healing, and most of the GCS machines were fitted with 750cc MAG engines as supplies of many British components had become increasingly scarce due to the war.
At this time their address was 307-311 Elizabeth Street, Melbourne, and they remained in business until 1941.
Post-war, sales of complete machines fitted with JAP, Reading-Standard and MAG engines resumed. The last of the GCS machines were assembled by Healing in 1923, and there were spasmodic sales of the marque until 1926.
The G.C.S. motorcycles were highly regarded and were among the best Australian-made machines of the day. Very few survive.
Stillwell is an uncommon name, but it appears often in Australian motoring annals. Bib Stillwell was a famous racing driver after the war, and went on to establish a string of motor dealerships selling Jaguar and BMW. He was also involved in aviation in no small manner, becoming president of Learjet in the United States.
Son of Bertie and Marion Stillwell, Bermar Sellars Stillwell was born on 31 July 1927 in Melbourne.
There does not appear to be a direct relationship between the two Stillwell families.
An aside. Bill Lear, who established the Lear Corporation, named one of his daughters Shanda.
Sources: graham64.wordpress.com which credits "A-Z of Australian-Made Motorcycles: 1893-1942", by Robert Saward; Wikipedia; autosport.com, et al