G'day all, I just found this thread and thought I would put in my 2 bob's worth.
In answer to Bob Carriere's comments about the chassis back in August 2006, it is my theory that GM Canada took a civilian pick up truck chassis of probably US origin and modified it to suit the CMP cab. The C15 chassis measures 36" between the outsides of the frame rails whereas the C15A and every other Chevrolet CMP measures 34" between the outsides of the rails.
You may also note in the pic Jeremy posted of his restored cab floor that the C15 cab has a different shape to the wheel arches. This allows the 9.00-16 tyres fitted to the C15 to clear when at full steering lock. The C15 has a much tighter turning circle than the 4X4 version.
Finally, congratulations to you Jeremy on the standard of you restoration. I have just started restoring my own C15 here and I will be very happy if mine looks like yours when I am done.
regards
Rod
http://users.bigpond.net.au/blitz_trucks/cmp.html