[blue00gt]

I have the BBK longtubes and Short-H on my '00 GT and I wouldn't wish them on anyone. The passenger side taps against the frame sometimes depending on what the engine torque is doing, the driver side rubs against my Borgesen steering shaft, and the collectors seem to be too far apart (probably why the headers rub) when you try to bolt the H-pipe up, resulting in an exhaust leak 3 out of 4 times that you try to bolt it up. The power gain was pretty impressive, but the quality seems to be crap.
I have heard way more quality problems with MAC than I ever have with BBK, so I would stay away from them also.
I noticed that Bassani, Hedman, and Hooker all make long tubes for 4.6s now, so you may want to look into those.
If you are planning on doing the intall yourself, it took me about 12 hours and a whole lot of cussing. The main problem is the passenger side - you have to jack the motor up about 3" and there is just no room to get your hands in around the 4 tubes to tighten the top rear bolts.