The torque plates being used by us here in the US are not as thick as the head itself. That would be very expensive, heavy and a waste of good aluminum. You just need something like Mike said. 1-1/2" to 2" thick or so (50mm or so). Then simply torque it down as if it were the head. I would not recommend overboring OR even honing an SR20 block w/out a torque plate. It is very easy for the applied pressure to cause distortion or any vibration/movement to cause the cylinders to become chamfered up top.