VLSD Rearend Question?

I have a 1990 240sx Fastback 5 speed and I want to do a vlsd rearend swap. I was told there are three different gear ratios and a speed sensor. What ratio should I choose, and is the speed sensor only for automatics?

Any input would be greatly appreciated.

P.S. I heard I will also need a new driveshaft, is that true?[/b]

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