Looks home converted to me. The Brough version based on the Austin angine had the engine longitudinally mounted & was shaft drive.
Looking again at the pics I was suprised to see it is twin carbed & open exhaust. Cooling looks a bit convoluted & I wonder if it has had a pump fitted, as I doubt that the original thermosyphon arrangement would work satisfactorily with what appears to be a much smaller radiator than a standard A7.
I would also have though performance would be a bit tame - depends on the age & state of tune of the motor, of course, but A7s were only 12 or 17hp at around 2800 rpm in standard trim.