My 1967 service manual has one big generic section that talks about lubricating things.

It says that below 10 F to use SAE 80, up to 100 F use SAE 90, and above 100 F to use SAE 140.

I believe this covers the steering box, differential, and manual transmission.

I think some people use grease as a fix for slow leaks on worn parts. I am not sure if doing it is a good idea or not.