9 inch Pros: Huge aftermarket support, non c clip axles, maybe find one with a limited slip. Availability, low cost Cons: 5 lug, stock axles are usually 28 spline, and it's a Ford. No idea what kinds of gears would come stock for most fords. My guess would be a 3.50. No idea on the WMS to WMS on fullsize fords, but I'd guess it's close enough. 9.5 SF Pros: GM made, six lug possible with stock parts, 33 spline probably easy to find with 3.73's or 4.10's Cons: c-clip axle, aftermarket support, expensive lockers??? could find one with a gov-lock. Availability?? Cost??? What would you run?