The Versailles rear end is 1.5" to 2" wider than a '65/'66 rear end so you'll have problems with the tires rubbing the quarter panel lips and even have the lips cutting the sidewalls. Nobody that has used that rear end in a Mustang has been able to make the parking brake work reliably. It's a futile battle.
The Versailles rear end is known as a 9" which is one of the strongest rear ends ever made. The axles have 28 splines on the inner ends where they mesh with the differential spider gears. Ford also made 31 spline axles that are stronger.
The Versailles rear end is known as a 9" which is one of the strongest rear ends ever made. The axles have 28 splines on the inner ends where they mesh with the differential spider gears. Ford also made 31 spline axles that are stronger.