
You might have to drill into the bumper support and make some holes. You might wanna contact Quamote from the other forums, he's the only other guy I know in the U.S. with a GTS bumper. Here's a link to his pics with install.
http://www.sr20forum.com/members-rides/144847-test-fitting-new-bumper.html
http://www.sr20forum.com/members-rides/144847-test-fitting-new-bumper.html