Mike & Euan whilst you have a good point and possibly just a tad of speculation (and I agree that Official documents don't always get it right!) the Danes seem to agree with the Figs. quoted in the Field Specs. I refer to the data quoted on this link...
http://www.armyvehicles.dk/chevyc60x.htm
i.e., Fuel capacity: 110 liter (24 gallons)!!!
I think there is a C60X at Emu Gully.....maybe one should ask the owners if the tanks are original and what is their capacity. A good discussion point nevertheless!
Rod