Sounds like you need an operators manual. I have one, and can look up info for you, but you might consider buying one. They are fairly common on ebay for reasonable prices. You can also get them from the Floyd County museum.  The originals are best, some of the reprints offered are not the best, but some are ok. The manual (BG) calls for the following oil spec for transmission, differential, and final drives:

                  Above 70: SAE 60 or 70
                  Freezing to 70: Sae 40 or 50
                  Below freezing: SAE 30