the T56 is a 6 speed tranny with an overdrive geared to where you could have 4.30 gears and still be able to cruise on the highway at a reasonable RPM
i'm not sure exactly what is involved but i've heard its really pricey, the tranny itself is about $3000
now for the kit,
www.stangparts.com has them for about $1600 with a used T-5
you can piece one together MUCH cheaper than that if you know what you need
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88 Notch, B&M Ripper, 3.73's, Ported E7's, Explorer int. w/ ported lower, pulleys, 1.7RR's, full exhaust,65mm TB, Nitto DR's, new best 1/4--> 13.42@106.18 (1.89 short time)