Maybe the extra capacity thing was an option or something?

I've had 12 '39 thru '46 trucks out here, all 1.5 ton or 2 ton, and have yet to have a tank that wasn't a perfect fit in a 1/2 ton truck.

I don't know how they could make the tank any bigger, tho.. maybe slightly 'thicker'?

an idea is only stupid if you think about it rationally.