Re: Ford axle info needed
This may help your decision - Go to the drag races, car shows, etc., you will see many vehicles (any make or model) using a Ford 9" 3rd member. Also most NASCAR vehicles use a modified Ford 9" 3rd member diff. You can pick one up from an early truck, have the tubes and axles resized, or even put larger axles in the housing. I have even seen one modified to be used in the front.
Check your 69, I don't think it will have 31 spline axles, but Curry makes a conversion kit to make it a 31 spline axle. You should also install a set of 4 spider gears (stock is 2). This can be a weak link with over 300 hp and/or low gearing. I am currently running the stock setup (28 spline) and have a NP435 tranny, 33" tires and 4.11 gears with limited slip. I have blown the 2 spider gear setup several times, but never trashed the ring-and-pinion, or axles. A set of lockers will greatly weaken this stock setup. It all depends on what you are doing with the vehicle.