I would assume they would work fine (I haven't tried so I can't say for sure). You'd be best off upgrading your valvetrain and computer along with them to take advantage of the addition rpm those cams can support but aside from that? I don't believe there would be any issue with a GS-R head and a B20 bottom having interference issues, the B18C1's combustion chamber is smaller but it shouldn't be an issue. Find a good deal on the ITR stuff or you just don't want to go with aftermarket cams?