[mr48chev]

Another vote for the 9 inch. Unless you just happen on the right rear axle housing that fits in your truck you will have to have one built but to me the advantages or running one are the ease of gear changes and the pressed on bearings on the axles.

Being able to just drop out the third member and swap in another one with a different ratio allows you to easily set things up for what you want to do at the time. Run at the drags put in some gears that will give you quicker acceleration. Make a 5000 mile loop around the US hitting different events and interesting sites for a month and in go the road gears that let you cruise at freeway speeds and pull gas mileage. One might not want to do that but the possibility is there just by having another third member on the shelf in the garage with the other gear ratio in it.

Bang for the buck probably the 8.8 that Jemezcruiser suggested as the right gear ratios with posi aren't hard to find, they often come with disk brakes and they are relatively inexpensive. If you don't like the gear ratio you are usually stuck with changing the whole rear or paying a shop to change the gears and set them up though.