Mike,
Tonight I've selected a photograph of an Australian Centurion taken by a Michael Jenkin. It's entitled 'Standing Guard' and the comment attached to it says "Coomandook - Dukes Highway - Centurion Tank ARN 169042".
The website that I downloaded this from gives a detailed history of this vehicle, the Centurion and its service in Vietnam.
Now let's see if I've learned anything about the Centurion over this past week. This vehicle is armed with a 20-pdr Type B barreled main gun with at least three, if not four, counter weights welded to the fume extractor. (They appear to have been welded parallel
and cross-ways to the barrel.)
The mantlet is not shrouded in a single piece of painted canvas like British and Canadian Centurions but has a closely fitting piece of canvas covering the main gun and exposing the co-axial machine-gun mount.
It's fitted with the 100-gallon auxiliary gas tank with the infantry phone fitted to its left side.
The barrel yoke, or crutch as you have referred to it, is open and leaning against the depression stop rail.
There is what appears to be an aperture inboard of the co-axial machine gun which may be for a .50-cal ranging machine gun.
There are two antenna mounts on the turret roof. I don't know if they are British or American type mounts.
Finally, as the turret reloading door is visible I would say that the forward bin box has been removed.
I would say it's a Mk 5 possibly with an RMG. What say you?
Cheers,
Dan.