This photograph inspired me to make an impression of the packs seen in use at Cape Gloucester:
Since first writing this post, my opinion has changed and I believe this is most likely a Paramarine shovel cover manufactured around 1943. There's a small chance it's a rigger made item, but I'm leaning towards the Paramarine style.
Jim Roberston provided me photos of his fantastic original Paramarine shovel cover. With permission, here's Jim's Paramarine shovel cover:
I found what some collectors consider to be an Australian made shovel cover - but I believe the item is just a bogus replica. I tossed it on the pack for the photo until I get a Paramarine example.
Here's the completed pack for now:
This concludes my efforts for now of accumulating the parts to assemble a Cape Gloucester USMC pack as seen in the famous photo.