The Factory Cafe Racers double down tube cradle frame looks like it was made for a 750cc parallel twin.
Odd too is how the center seam of the UCE crank case is offset to the left of the center line.
My gut hunch is that when the P twin is finally unveiled it will be UCE technology based, use as many off the shelf parts as practical and be nestled in a version of the Cafe Racer frame.