I'm sorry you took offense at my post Don. I was merely pointing out an error of fact.
Insofar as the Bren Being Coaxially mounted on the Marmon Herrington Mk 1 and Mk II cars, that Boyes and Bren are likely NOT mounted on the same mount. Certainly they are facing out of the same face of the turret, but I strongly suspect, given how the RAC and it's various contributors never mounted brens on 'fixed mounts' ala a BESA or AFV version of the vickers. Looking closely, you'll see that the MH MKI and MK II cars were fitted with a Ball mount for a vickers and a fixture to take a Boyes on the MKIIs. The Vickers MMG ball fixture was removed and replaced with a point for a bren, presumably to use the Vickers in the Flexible role.
You'll note that this photo, shows the BOYES at elevation and the Bren at a straight depression. This is a preceise example of a mount that is NOT coaxial. Co-Axial - Same Axis. On AFVs with a coaxial mount where the weapons are controlled by the gunner, they both move, that is to say, elevate (and maybe train) with each other on the same fixed mounting. Though, admittedly warwheels uses the same term incorrectly.
Suffice to say, I'm strongly inclined to understand that the MH Mk I and MK II cars had a pad for the base of the receiver of the Boyes and Bren (in the case of the MK II) to sit upon, similar to that which my Dingo has or which my various friends Bren Carriers have.
My point still stands, in the close confines of MOST afvs which have a roof over the turret, a Bren would be awfully difficult to service and operate. The barrel handle necessitates far more of the weapon inside the turret and the magazine changes are exceptionally awkward. The Bren also lacks a mounting for which to fix it to in an AFV. One COULD use the mounts which are used on the tripod, but that would mean a VERY long and very obtrusive mount from forward of the barrel handle and just under the buttstock. I've handled a Bren in an AFV, a fixed mount would take a great deal of room. That's why the British just put them on pads on the front of the AFV or entirely outside the vehicle as on a PLM mount (Humber SC).
Compare the MH or Humber/Morris LRCs to the Vickers and the gun mounts on the vickers are clearly a an elevation only mount with the .50 and .303 vickers guns elevated on the same fixture with the same outer mantlet protecting the guns. They do not elevate separately and they are co-axial. Suffice to say, with those large water cooling jackets, it's quite clear that those are NOT Bren LMGs but Vickers MMGs fitted. One a .303 the other a .50 (note the larger cone on the .50).
Insofar as the Humber AC's go, I could not recall if they were incorrect or not. I did note that the MK III had the wrong crew count. I was articulating the weapon fit for completeness.