The Turbo400 is a 3 speed. You will have to run some lower gears or way taller tires to get any mph out of it. Plus some Torque! Anyway, you will give up all your streetability with the ultra High stall speeds. The bands always slipping will cause trans fluid temps to get really hot. Then you screw up stuff. You need a good gear box. Possibly a 4+1 doug nash or a Richmond 5 speed. They would be your cheapest options. Other than that the Dog box is also an expensive option.
Do a T2 rear chunk and some chromoly axels in the rear and you should be fine with the IRS. Go until you break it I guess
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