The GT3 destined for North America doesn't have many of the options that the Rest of World (ROW) versions do. I wanted to order the Club Sport edition, but apparently this isn't approved for US use. The US seats are the standard sports seats vs the non-adjustable carbon fiber GT3 seats sold elsewhere (saving 40lbs *EACH*). 80lbs savings is a fairly large performance increase on any car.

Eric Bosco has details on GT3 seat installation which should make the process easier. For more info also see instructions and photos of the full GT3 installation process, along with gotchas to avoid.