A new version of dev-lang/R has been released from www.r-project.org. The new release is 1.7.0 and the old one in portage is 1.6.1. I conjecture that the ebuild basically needs to be changed to point at the new source tarball. At the moment my ebuild skills are nonexisting so I havn't tried to verify this conjecture. If testing needs to be done do not hesistate to contact me.
*** This bug has been marked as a duplicate of 21448 ***