The machine gun in question is one of several versions of the Vickers machine gun modified for use on Armored Fighting Vehicles. It could be one of the following versions - Marks 4B, 6, 6*, or 7. It is most likely a Mark 4B or 6 as these entered service in 1934 while the other two types entered service in 1938.
These types were also used on British light tanks of the 1930s thru WW2. The following website will give you info and pictures on each of these versions of the Vickers.
As far as dimensional data is concerned, I only have a small blurb on these guns in the WW2 Fact File - Machine Guns by Peter Chamberlain and Terry Gander. There is also some comparative data on Mark 1.
Mark 1 Data
Overall Length - 45.5 in
Barrel Length - 28.4 in
Weight w/water w/o tripod - 40 lb.
Mark 7 Data
Overall Length - 43.3 in
Barrel Length - 31.1 in
Weight w/water - 47.2 lb did not use tripod
Caliber for both is .303 in.
I hope that this helps.