PS-
The ford 9" is a popular rear end with racers and hotrodders alike for several reasons-
You can change the pumpkins cheaper and easier than swapping the ring and pinion in a chevy differential.
The ford 9" is everywhere, so parts are easy to find.
The ford 9" is easier to 'set up' than chevy differentials, ie adjust the pre-load and lash.
The ford 9" does not use the chevy 'c' clip desigh to keep the axels connected to the ring and pinion and otherwise in the car. Occasionally the c clip on an chevy diff will break or come off and the axel will come off the car along with the tire. I've never seen it, but I've heard about it. It is for this reason that NASCAR requires either a ford 9" or 'c=clip eliminators' in a chevy diff.
GEAR RATIO- Try the search function here for more information on this point. Basically, your rear diff gear ratio is determined by your planned use for the truck, tire diameter, gear ratios on your tranny and the torque range/power band of your engine. So, if you are planning on hauling a trailer and have the original 4 speed you'll want something different than if you are using an automatic and planning on just zipping around town.
