The top plate in the picture above is magnesium printer's plate. It keeps the weight down for my back's sake, since I cannot get this gross assembly into my honing tank, and must do in on the floor in a drip pan I have made to hold it by the top plate. The bottom plate is some kind of aluminum billet. I found that the top plate gives very little distortion of the bore or valveseats at 55 ft/lbs.
But the bottom plate does this even at normal overbores, and much less torque (28 to 32 ft/lbs):
You can see the shadows where the Sunnen stone sweeps over depressions caused by the fastener torque. This is NOTHING compared to the distortion of Harley cylinders! (H-D's big spigots must give the fastener stress something to push against, plus I torque them at 40 ft/lbs.)