Belonged to the 'Everymans' organization, I think the mil support arm/alternate but more common name of Campaigners for Christ (like 'Red Shield' of the Salvoes). Shipped to SVN Oct 66 on Jeparit, RTA Oct 71 on Sydney. Listed on page 168 of M&D.
Getting back to 'BMSS' for just a moment, AGAS 5 was correct: it is the Box Metal Shipping Steel, NSN 8115-66-025-8558. It was 8 feet x 6 feet x 6 feet 4 inches, with a volume of 260 cubic feet (volume was mentioned in an earlier post). Cargo loading was maximum 10,000 pounds. Officially introduced into service in late 1967. 250 in the initial purchase.
Nice pic: as always, Tommy, you come up with some significant images!
Mike C