Help with rear gears for a 1st gen with t-56

[68firehawk]

I know there is other threads on this but none for my exact circumstance.

So i've decided on my rim and tire set up and im currently haveing my axle shortened and set up for the car. So that means i'm to the curtial point of choosing gears. I'm thinking 3.89's will get me to exactly where I want to go but I would like some more imput on the matter.

I have a full floating 31 spline 9"
Tires are 335/35 R 17
My LS1 will be well over 450 horse

I would like to be able to do 200+, cruze comfortably at 75 or 80 and scare myself in the first few gears. Is this possible? I would like to keep from having the gerbox altered, for now.

and does anyone know where I can find a gear ratio calculator?

Thanks

Jake