Terry
The data plate is not the easiest to read in the photo.
The serial number (VIN) of the vehicle appears to be 4844521304.
The "SM6407" (SM not SN) is the British Army contract number. Supply Mechanization 6407.
I have a copy of a 1944 Census numbers list from Chilwell in UK (via John Marchant about 30 years ago) listing ALL British WWII WD number ranges to that date but as the list was poublished in Nov 1944, it does not show the 1945 contracts.
This truck probably was never delivered to the British. One turned up in Czechoslovakia (pictured in the now defunct Wheels and Tracks magazine years ago). My friend, the late Peter J. Ford of Saskatoon SK, found a rear door and some other parts for one of these C8A HUP staff cars in Manitoba (from a vehicle that had been hit by a train as I recall?) and those went to the restoration of another such vehcle in Canada.
These HUPs probably came out of the CMP stocks held post-war at MacDonald in Manitoba.
Colin