Gear Oil for 4 Speed?

When I swapped tranny in my 1965 Mustang I had to use a special classic GL4 gear oil because it has brass components. Do I need any special or specific gear oil for the 4 speed in my R112?

Just use SAE 40 or 50 engine oil and call it good. It is what heavy trucks used for years.

Done. 40w was a lot easier to find so that’s what I used. Thanks.