Thanks.
I don't think I can make it any narrower.
The engine height isn't fixed yet (sub-frame for drive train), but to really lower it the primary drive will run up-hill a bit so that the transmission sprocket/swing-arm/axle line is still good. This is preferable to horizontal primary with the angle at the swing-arm pivot pointing up to the axle, yes? It's a monoshock so the suspension rate isn't limited to shock travel from the arm.
I know that simply moving the axle back will reduce traction (i.e., unload the rear wheel) at launch, but it also creates a place for ballast (battery, oil tank, window sash weights). I have less than 100 hp to start, and I think I can safely limit power in low gear to make it easier to ride.
Never having ridden a long wheelbase bike, how much stable is it at 80" than 68"?