rear end shifting to much

[myred86gt]

I've recently put in 373 gears and have noticed some rub marks on my rear pipes
from the tires. Seams like the rear is
tweaking quite a bit from the increased
torque. Any one have any recommendations
to fix this problem? I heard that urethane
bushings can bind, is this true?
Will a tbird tbocoupe rear bolt into my car
without any hacking? I heard that these are
1.5 inches wider than the mustang rear.

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86gt flows, prochamber, shorties, fpr, 373s
steeda triax, fms hd t5, al drvshft, jacobs
ign., k+n, kirban fpr, E7s, Explr upr + lwr