I am considering swaping to a 9 inch because of my busted 44 pinion and I had some questions

Definetly going spool. I don't like the detriot that much and I use twin sticks to drag the rear around when needed.

4.56 gears. I like the crawl ratio that ive got with the dual cases

35 spline shafts

now for what brand of gears. I have always heard good things about richmond gears and I saw that mark williams sells them with a 35 spline pinion. That should be alot stronger than the stock 28 spline pinion.

not sure what to do about the center section. nodular iron is what I was thinking.

Oh and where to get good 35 spline shafts