There is an easier way, and it looks like the 2 in Keightly have been done with the East Bear kits. Obviously that just going by the pictures.
To go down the route of a full GTR front using OEM GTR parts is not something I would recommend. There is a lot of work involved getting them to fit the GTT and will cost you way more to get them fitted than the parts cost to buy. Your looking at GTR bumper mounts, front bumper, front wings, bonnett and bonnett hinges.
Check out
http://www.east-bear.co.jp/SHOP/R34ST15.html.
Just a quick word of warning, they are very expensive. For the full kit you will probably look at spending over £1000, not including shipping from japan and Vat & Customs.
Also,
www.neweraparts.com have some of the kit on their website and they are traders here. What ever isnt listed on Newera's site just email them, as they can source if from East Bear for you.
I have an East Bear front splitter for my Aero kitted GTT. The quality really is worth the money you pay.
John