That means that some Oz suppliers could have had local content/'manufacture'.
Yep, very much so. Sun fittings were used on a much larger scale in Australia than R Walker & Son, and prior to WW1 you could get real Sun motorcycles, Sun motorcycles badged and sold as local product, and local machines assembled from Sun fittings that often looked similar to the "real deal", but likely had locally built tanks, guards, handlebars...
RWS was probably a similar thing on a smaller scale. In 1919, RWS fittings were actively advertised and there was an agent in Sydney - see the advert from the Motor Cycle Overseas Supplement from Nov 1919. The post-war Excelsior Villiers announced in March 1919 was likely built from the RWS set. Local builders - Elliott Bros in Payneham, South Australia, for example - used the RWS set with a Villiers engine to make their Elliott motorcycle. I'd be pretty sure they brazed up the frame, and used locally-sourced tanks, guards, handlebars etc. The certainly stamped their own frame numbers on the resultant machine. I've not seen the "true Excelsior badged as an Australian make" from this era, but we know that it did happen from 1930 with Waratah.
Frame numbers are often the key. If a Sun-based bike has a Sun frame number, it likely originated as a complete machine in the UK. But a similar machine, with a local frame number, was likely assembled locally from imported fittings. Some surviving Australian frames use fittings from more than one manufacturer.
Back to Excelsior. Grace's Guide had two pages relating to RWS:
https://www.gracesguide.co.uk/R._Walker_and_Sonshttps://www.gracesguide.co.uk/R._Walker_and_SonNot everything there is exactly correct: by the time that "R. Walker & Son, King's Rd, Tyseley, Birmingham" were advertising their frame sets in Nov 1919, Bayliss, Thomas & Co., makers of the Excelsior prewar, had already moved from Coventry to "Excelsior Works, Kings Rd, Tyseley, Birmingham". See the advert announcing the move from Sept 1919.
Presumably this is the factory of interest.
Leon