RE: Manipulating aileron linkages for perfect rolls?
I would say the relationship to the aircraft's longitudinal center of gravity is more of a concern than the relationship to the crankshaft. An object in free space will rotate around it's center of gravity (center of mass) in whatever axis you choose. To not do so requires an additional force. So for the aircraft to happily roll about the engine crankshaft line the crankshaft should be on the longitudinal CG line.
Trying to compensate with fancy aileron throw manipulation may result in rolls at one airspeed that are fairly axial, but to the best of my mental figgerin' this situation will deviate at lower or higher airspeeds. I think it is better to think CG line location.
Note to aero engineers - I am using the term longitudinal CG because that's all I can think of, it might have a different term associated with it, but hopefully what I mean is evident. The longitudinal line that passes through the center of mass.
MJD