I don't worry much about the left to right misalignment positioning of the motor due to the tranny U joint needing misalignment for it to work properly on the needles bearings, if it is off some it makes the needle inside move and rotate more.
As far as the angle of the carb flange on the intake manifold that changes a tiny bit when you climb into the car, doesn't it
It is really nice to get as close to as you want it as possible so you are happy with your work