Definitely a post military mod and not a bad one at that. As Hodgo said above, an F2 tray transplanted on to a Mk3 chassis.
When the military was experimenting with tippers in the early developmental stages they stuck with dual tyres (1000x20's) rather than the more common (to the army) 1200x20's.
The early prototypes to the F2 were also fitted with duals rather than singles. This idea was dropped prior to production as it was found to offer no great advantage with the tandem axle setup either traction wise, floatation wise, or deflection wise.
The trays on the teaspoons were a smaller tray than the one pictured and the headboards were a different shape (straight up and angled at the top).
Any Mk 3 is definitely worth restoring but preferably back to its original "trucks cargo 2 1/2 ton GS" specs.
Regards
Glen

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1950 S1 80" (Sweetpea)
1963 2a gunbuggy 112-722 (Onslow)
1964 2a 88" SWB 113 251 (Daisy)
1965 Mk3 170-937 (Von)
Track Trailer (RAAF) 200-166 (Richard)
Daily driver now another brand!!!
REMLR 226