I didnt have a bit of trouble with the bbk longtubes on my 99 GT, installation and all. They fit like a glove, no noise. I used the factory studs except for three places where the tube was in the way. I highly recommend getting the Percy Seal-4-Good gaskets from summit for the 4.6L for $40.00. Theyre aluminum, wont blow out, and seal great (might as well do it right the first time). I lifted the motor about 4" on the right for clearance, and about 2" on the left just for alittle more room, though I probably could have left the left side hooked up.
It gave it a cool burbling sound and a seat of the pants feel, and I went from an offroad H and manifolds to an offroad H and longtubes.
For what its worth, I have a friend with MAC Longtubes on a 98 GT, and he had to "massage" the floor on both sides with a hammer to get the o2 sensors to stop tapping the floor. I had no problem with the BBKs. If you try denting the floor, make sure to disconnect the battery for several minutes first so you dont deploy the air bags.
Tim
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