Thanks for the replies folks. Much appreciated.

The AP seems to confirm once and for all that the twin Brownings were on a Rose mount.

On the subject of W8315, the references I have say that the turret on this airframe was designed by Rose Bros, and was a one off trialled at A+AEE. Strangely, it looks (externally at least) a little like the Bristol BI turret.

Cheers.

Tim.