I have the gear vendors unit with 3.55 gears. It works great but you may have to messaage your tranny tunnel plus make sure your pinion angle is right. May have to shim your rear axle for the correct angle.

That being said. I don't see how you will be able to use the unit as a six speed. It has a slight delay when it shifts. How do you expect to shift back down exactly when you shift up to 2nd gear. I just use it as an overdrive and I will use it to split 2 and 3 gear when racing.