Michael, if you find a book by Ian Skennerton titled " Australian Service Machineguns", you will find pictures. Australian Thompsons had the same modification, as well as the forend sling swivel relocated to the left side of the horizontal foregrip. However, they didn't use ( to my knowledge) the Kerr sling. Rather, the SMLE .303 sling was used, which should be in plentiful supply still. Hope this helps.
Regards,
Ken