C60 cwt Signals CZMk IV

[Gordon Yeo]

Here are some pictures of the truck I bought from Greg Wright. From Bill Gregg's book "Blueprint for Victory" page 121, there is a pictures shown of a truck, Body Design 5J7 - C60 cwt Signals CZMk IV. The van body has the two outward swinging windows on each side, as well as two small outward opening doors on the lower front corners. Which is a description of the van body shown here. Does anyone have any information on this Mk of truck? What it was used for? Interior layouts? etc.
I have another C60 Machinery chassis that has bonding straps between the body panels similar to a wireless truck, and the C60 cwt Signals CZMk IV has none, could this be some tip off as some use other a wireless/radio truck

Gordon