The B18C1 head actually has a smaller combustion chamber, so if you put the B16A/ITR head on it, it will loose compression. The best way to get that back is new pistons. A thinner head gasket will work, but you may loose some of the reliablity. Personally, I agree with Bumnah and Shivers. For the same money as the ITR setup, you could go with Skunk2's stage 1's, valvetrain upgrade and their ITR copy IM and probably stomp the ITR setup into the ground (higher compression and more aggressive cams).