Rob,
When you say that
"I don't believe it's a tracked truck diff, the plate looks well made & machined, not a farmer throw together.", I think we may be getting our wires crossed. I think Tony Smith means the "Truck, Tracked, 1 ton, GS", which is a throwback from the Carrier development project.
When you said that there once was a Blitz with wierd brackets on the chassis that's what made us all sit up and take notice.
I am now tending to believe that it might be the correct sprockets...but tend not to think that they are the sprockets for the "Tracked truck"
Photo with thanks to Keefy.
http://www.oldcmp.net/tracked_truck.html#Anchor-49575
Pedr