[Grant Bowker]

It is on 20" wheels which could be as simple as the owner likes the look or indicate heavier origins.
The fuel tank looks like it has the proportions similar to C60X that I believe shared the larger tank with the CGT, but it is hard to tell from 1 photo.
The spare tire carrier does not look familiar, but that could be my lack of knowledge. It does look easier to load than the production models I'm familiar with, particularly for one man use.
The body looks as if it either has minimal space for suspension wheel travel or it has wheel houses internal to the box with no sign showing outside which is not normal for a Canadian made box. Another possiblilty is that the curved mudguards (not usual on Canadian steel bodies) continue into the box to make a round wheel house, I am not familiar with a body like that, at least as Canadian steel production.
The front maker lights don't look original, but are probably more visible, safer and may be a legal requirement for registration in the owner's area.

Most parts of the description seem truthful taken one piece at a time. It does seem to be CMP, Chevrolet is possible, CGT could be the origin of chassis and cab back to rear of door, it is cab 13 style (as opposed to 11 or 12) however I'm not aware of the precise configuration shown being a production variant gun tractor. In the end, it's the owner 's truck and they can do what they want with it (at least in my opinion), particularly since they don't seem to be deliberately misleading. The truck looks in a state that says someone cares about it, it shouldn't be headed to the scrappies any time soon which might have been it's fate if left waiting for a perfectly accurate restoration. Who knows?