A pertinent page from the 1954 Truck Operator's Manual.

Late in 1954 other grade oils were recommended.

I have used 10W-40, 15W-40, 20W-40, and 20W-40 (in an old engine). I think I am now using Rotella multi-grade Diesel truck oil.

Recommended oils for pre-54 truck engines (low-pressure 216 and 235) might have been different.