1946 Oliver 70RC

In the service manual in the lubrication section it talks about using 'transmission oil' in the transmission of the tractor.  It is talking about a straight weight oil, correct?(we're not talking dexron/mercon?)  What kind of oil do you normally use?

And to check the level of the transmission oil, you remove the transmission oil level plug and the oil should be up to the level of the plug opening-is that correct?

Thanks in advance.