I have a shortened Dana that was originally from a 69 GTX. It has never had fluid in it since it was shortened. I need to get fluid for it and have some questions. What type/brand of fluid should I get and how much will it need? Also, if it matters, the Dana will be used in a street driven car, not a race car.

I'd get 4 qts of garden variety parts house 85-90 wt hypoid gear lube and a little bottle of Mopar or furd sure grip additive

I was told the Ford friction modifier was the way to go with a Powr-Lok to prevent chattering. Your Ford dealer should stock it. It's reasonably priced and pretty slick but be warned, it's some rank smelling stuff.