OK: it's weird I know but I have made a study of Excelsior frame lugs. Perhaps not as late as the bike in question, but I think the same ideas apply.
Prior to WW1 the firm of R. Walker & Son were makers and wholesalers of frame lugs and fittings. One of their large customers was Excelsior, which at the time was still attached to its origins as Bayliss Thomas. During the war (1917-ish, I recall), RWS purchased Excelsior and I think their ownership carried on until "the end".
Thus "Excelsior" "made their own lugs and fittings" while RWS sold similar lugs to other makers, in the UK and (especially) the colonies. They offered lug sets for a range of bikes, both in the UK and in Australia. In Adelaide, for example, the lightweight set was used by Elliott Payneham for some of their Villiers-powered bikes while J.N. Taylor used the heavyweight set for their V twins. My 1921 Victor Blackburne, made by Taylor, has stamped on the engine plates: "RW&S 6&8 JAP 8 B". My bike uses the 8hp Blackburne twin, while others (like the bikes built by Taylor for Swastika) use 6 and 8hp JAPs.
Unsurprisingly the Australian bikes share many features with the Excelsiors of the period. When Excelsior went to a whacky enormous steering head castings for their big twins around 1921, the same big lugs appeared on some Australian bikes, like Lou Borgelt's personal Swastika JAP.
The RWS heavyweight gearbox lug (or Australian copies of it) appear widely in Australian bikes in the early 1920s.
The Waratah on sale looks like it has a star dropper welded to the front down tube!!
Leon
Edit: I have only a couple of illustrated adverts for R Walker & Son lugs and frame fittings, from 1919 and 1924, both showing lightweight sets. Because sales were wholesale only, adverts don't appear in the usual magazines. Happy to see more if there are any out there!