Having spares in pairs or cost isn't the concern. I am used to minimizing spares where I can from my days of racing offroad. Simply put, I would rather have equal length axle shafts if I can. That way if I am at the drag strip and break an axle shaft, I can swap it out and keep running. If I break another axle shaft, I can swap it out and keep running because my pair of spares work on either side. If having equal length axle shafts causes an issue due to putting too much offset to the pinion, then I will build the axles to have zero to factory offset and stick with unequal length axles.
