What type of Differential oil?

RustyRatRod said
80w90 with Ford friction modifier.

conventional or synthetic? or hypoid btw do you know what hypoid is? I cant find it anywhere.
Except this Castrol gear oil mentions hypoid: https://www.classicindustries.com/product/1976/dodge/aspen/parts/cc1840.html

And I forgot some say GL-4 others GL-5. Does the "GL" matter