An interesting article on the use of machinegun Carriers in the desert in 1940 - 42
http://anzacsteel.hobbyvista.com/Armoure...stph_1.htm
of interesting note is
"The volume of fire that the carriers were able to produce, with their Vickers guns connected to the engine radiators of the carriers, was largely responsible for minimizing the infantry casualties"
Seems to clearly indicate that the Vickers were used mounted in the vehicle. This would make sense considering the mobility of desert warfare
I am unsure that the vickers would cause the Vehicle to move when fired as it did weigh 3.8 tonnes unloaded, and when you consider, full crew allotment and kit it would have weighed over 4 tonnes in combat. If the Vickers was intended to be used, connected to the radiator, and provision was made for this in the vehicles design then it is doubtful that this would be an issue.
Oh and to even it up a bit I found this nice Canadian website
http://www.canadiansoldiers.com/mediawik...l_Carriers
In relation to the Oxford Carrier used in the post war years, this was actually a M5 tank with the turret removed and converted into an APC. Which is essentially what the Americans did when they created the M39 AUV (Armored Utility Vehicle), which was an M18 Hellcat with the turret removed. Both saw extensive service in Korea.