The current ebuild of gimp-print-cups, gimp-print-cups-4.3.8-r1.ebuild, does not create the symlink libgimpprint.so.1 pointing at libgimpprint-4.3.8.so, which causes ghostscript to fail. I manually creating the symlink and it's working.
will have a look .. sorry for the delay there was a problem with the mail alias so i didn't get the Bugzilla mails
gimp-print-4.3.18 now in portage fixes this.