6x6 cmp gun tractor

[Hanno Spoelstra]

The Canadians worked on a 6x6 gun tractor on a GM C60X chassis. My guess is that prototype is depicted in your drawings.
The Australians toyed with the idea as well, as can be read in Mike Cecil's article Chevrolet C60X in Australian Service:

There is a strong possibility that the Army also had a pilot model heavy artillery tractor built on a C60X, but unfortunately no details about the project have been located as yet. Interestingly, one chassis number, 28660M000012, is ‘missing’ from an otherwise unbroken sequence. If that chassis was used as the basis for the experimental heavy artillery tractor, then Army would have received a total of 121 chassis, which is consistent with the order for 120, plus the pilot model chassis.

More will undoubtedly be added by others.

HTH,
Hanno