Not sure whether the "S & L' was prototyped as a "concept" before further formal "trial" production, BUT there is (was) a drawing at Lithgow that shows BOTH variants (short and intermediate).
I will see if I can dig out the reference number for it.
There were definitely a significant number of drawings prepared for the special barrel and rear-sight / modified charger bridge.
Furthermore, it was not "Shortened and Lightened" just for jungle-bashing, but was intended for use by airborne troops. It was thus the platform for the famous "Machete Bayonet", itself correctly called, "Bayonet, Parachutist", and noted as such on the factory drawings.
Some of the other "short" Lithgow '07 bayonets are also tied in with this project, and with the concurrent development of the "Owen" SMG.