Adding Tru Trac to 489

Changing to 3.91 and adding Tru Trac to my 489.
I see 30 and 33 spline axles listed, with the 33 spline being more expensive. Any info on that?
As well as the spline count on my pinion. I was hoping to not have to take it apart and leave it apart for a week.
My memory isn't what it used to be.