Well after a long wait, and a lot of patience i finally took the plunge and attempted to fit a 34 GTR exhaust (Impul) with stock GTR cat to my GTT split dump/front pipe from JJR.
Several hours and a broken turbo stud later and its on, but...
I can now confirm that a gtr catback (at least the one i bought) does NOT bolt up to a gtt, it is infact too long! its about 3/4's the length of the cat too long, so about 8-10inches
So now as it sits, i have my JJR 3" front/dump, mated up to the mid section of the cat back, minus the cat, with about a 8-10inch piece of custom pipe to make up the difference in length, which then joins to the end pipes/muffler
Further more, when i get a new cat, the system will no doubt need a little chopping and changing to accomodate the size, assuming its longer than what is already there.
So no, a gtr catback will not bolt up to a gtt without a little customization.
Big thanks to all the guys at Al's Race fab and mechanical, worked tirelessly through the night to get me back on the road