If they were for GTR, still possible to install on GTT. The only thing differencs is the length of your cat (or decat) pipe joining to the downpipe flange. Can ask any exhaust shop to fabricate it cheaply.
The McLaren MP4-12C has a lot to live up to, particularly since it was made by the very same company that gave us the McLaren F1 and subsequently the racing version of it, the F1 GTR.
for those who are planning to upgrade to aftermarket H/U, this is the item u r looking for..... since i sold off my ride, the h/u fascia plate is for sale....... its totally new and have not been installed...