Thanks,
This is my limited knowledge on the vehcile.
The Guy FBAX was one of many 3 ton 6 x 4 vehicles produced by the British during WW2. In fact the 6 x 4 chassis was first produced in the mid 1920s and was a design favoured by the War Office. By the outbreak of WW2 the 6 x 4 was considered to be obsolete, the newer 4 x 4 being favoured, but 6 x 4s remained in production throughout the war. Sometimes referred to as rigid six wheelers many were used for specialist bodies and for bulk load carrying such as pontoon, bridging and derrick equipment.
Data from:
British Military Vehicles WW2 by David Jane
British Military Transport 1829-1956 by David Fletcher
Yes, infomration is a bit scarce.
I do have the vehciel specification if that would be of any help, but I imagine you have that already.
Alan