The shop manual states
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0004.htm
"Every 1,000 miles put a few drops of a light oil, or engine oil, in the two oil cups.

If using a modern/replacement front bearing some chance it is sealed and greased, would not accept oil. The rear unless changed would be a bushing and would like oil.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-