The correct lube for the tranny is SAE 90 transmission or mineral oil.
Shown Here on page 47
The transmission was a Chevy design built at the Muncie plant.
The 4 speed would have started with "4" in the model number. Early 4 speeds were SM-420 and later were SM-465

Kevin
1951 Chevy 3100 work truck
Follow this saga in Project Journal
Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.