You'll get a better gain from the cams, the P72 GS-R head is slightly different the yours with no serious advantage (plus you have to use a funky intake manifold with it) and the PR3 Type-R head has better springs and cams, and slight porting... again, not worth the effort when your head with a couple new cams will outflow it anyway.

Don't forget the PR3 GS-R head, it's identical to yours but still came off a GS-R (92-93, B17A.)