Ford 9" in 1965 Barracuda...an option?

I have 9” out a Lincoln Versailles. Fairly easy to install. I adapted e-brake cables and had a custom driveshaft built. 9” fords parts a lot cheaper and easier to find than 8.75. Due to the configuration of the ring and pinion you will need the proper gear oil from Currie.
Why Run Conventional Gear Oil?