Well, whadya know. Give him the money Mabel.
From Wiki -
He wanted a competitive British engine to put in his cars so Leo designed him an engine which was essentially four Manx Norton engines put together. Thus a 200bhp engine was directly available. In fact, the bore and stroke (86x86mm), cam profiles, head design and even four Amal GP carburettors were the same as the motorcycle engine but the engine was water cooled and mounted on, of all things, a Rolls Royce cylinder block.