Remember that the GTi-R combustion chamber holds more volume than the other DE's, DET's. Because of this regular caluclations will be about 0.2 points off. For instance the 300zx pistons will only give a 10.8:1 CR (from my calculations)
With the 1.2mm head gasket your compression ratio should be 8.4:1 CR. If you get a Tomei 1mm head gasket and the 300zx pistons that should net you an 11.1:1 CR. You could always get some
Wiseco makes some 11:1 CR pistons for the DE. This would yeild a 10.9:1 CR in the GTi-R motor. With the Tomei 1mm head gasket you would get 11.2:1
Not worth it for that extra 0.1 points but the option is out there to use forged DE pistons, they will need to be machined to clear the oil squirters.