first of all, welcome to the site... but pelase post in the right forum. this is the bullshit forum, not a tech forum.
secondly,
b18c Spec R is not the b18c5.
b18c/R is the JDM ITR motor. and yes, it is a little different from the US version.
the jdm version has a better 4-1 manifold, stiffer outer valve springs, 4.785 final drive vs. the US 4.40 tranny, and of course, the red valve cover
i might have missed something there...
at any rate, a gsr vs an itr have some differences, mostly in the head, and compression. the gsr has a block girdle, the itr doesn't. the itr has a better intake manifold with out the gay 2ndary butter flies, as well as larger cam profiles.
there's a bunch of difference, all small, but let the ITR add up to more power.