How necessary is a gear install kit???

I'm going to be getting some 4.10's installed sometime soon and right now I am buying the parts that I need. I am getting FRPP 4.10's, SpeedCal, and I have Ford synthetic rear-end fluid. My question is, I have seen the gear install kits that range anywhere between $40 and $120. They include (depending on the kit) new shims, bearings, ring bolts, crush collar, etc.. Should I, or do I need to, buy one of these kits. I was looking at the "B" kit since I have almost 50k miles. What did you all think? What did you do on yours?

Thanks.

I linked the kits below for reference.

http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=5962

http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=5956

http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=5957