Don't write off a properly set up T5Z for a stroker street SB. Had mine set up/blueprinted by Liberty Transmissions. 1st geat is just right 2.95, 5th changed from .68 to .80. With 3.55's, 2500 RPM=75MPH. Aftermarket cable clutch linkage (BBK) works perfectly, and doesn't have any
oil in it to leak.
Again, with a light car like a Cobra on street tires, you usually spin the tires before overtorquing the trans. If you beat on it a lot, you'll eventually break it.