You want two with the mains torqued in place and both torqued in place when you are honing the cylinders, at a minimum. The superstock racers go to great extremes with this and will bolt everything else to a block and then map the cylinders from underneath with the heads torqued on and try to duplicate the mapped measurements by adjusting the bolts on the torque plates. Running hot water through the block during honing was mentioned by OldManMopar, those are the guys that do that sort of thing.
