Hi Tim!
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This is a Canadian Military Pattern vehicle, built by Chevrolet, a brand of General Motors Canada. Based on the Chevrolet Gun Tractor (CGT) 101" wb chassis, a small number was built as a 2-pdr AT Gun Portee. They were fitted with the second model cab, the No.12, placing it in the ca. 1941 timeframe. Pic below shows what they looked like after assembly in the UK. Full story in one of the back issues of Wheels & Tracks magazine; more pics and info over on the Maple Leaf Up Forum.
As for rarity, a fair number somehow has survived. An identical vehicle was
offered for sale recently on this site. Maybe the former owner is willing to let us know how much he sold it for?
Nice find, I hope it will be rescued for restoration someday soon!
- Hanno
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