C60L tanker truck

[Grant Bowker]

Thank you Ivan, I hadn't thought to count the manholes. I see one on the water tanker, two on the gas tanker.

Although the angles the photos were taken from weren't meant to provide this comparison, the gas tanks seem to be taller - close to the height of the cab while the water tanks were lower (fits with the smaller capacity of the water tanks though both are built to use a long chassis). As far as I can tell, only the 5K1 tank (and none of the water tanks) had the permanently mounted hand rails on the tank (also serving to hold a tarp for camouflaging the extra value of the fuel cargo). The later petrol and the water tankers had tarp superstructure mounted to the catwalks which would give a wider shape, closer to a GS body (with the superstructure in the low position).
Hanno, the photos aren't large or clear enough to either prove or 100% disprove a front mounted or side mounted exhaust with certainty though if the exhaust were mounted to the underside of the bumper I think it would have shown in at least some of them based on what can be seen.
On balance, I think the original caption writer is correct - 800 gal gas/petrol tanker.