treegrower - Below is a pic from the 1948-51 (info same through 1954) Chevrolet Truck Shop manual to show where the stamped rear axle ID number is. You may need to do something like the suggested guidance in this Legacy Tech Tip
Reading Indented Numbers to help you read what's on the axle pumpkin.
Bill Hanlon is correct on the standard rear gear ratios for the 1/2 ton for 1953 (and earlier) and 1954 axles. The decider on what yours is will be from decoding the stamped ID number.
If it has a prefix of "M" it's a 1954 1/2 ton model year. "L" is for 1953 1/2 ton model year. "K" is for 1/2 ton model year 1952. "J" is for 1951 1/2 ton model year.
The unit number will consist of two letters, the first being the model year and the second being the plant it was built at. That is followed by one or two numbers indicating the month built and then followed by one or two numbers to indicate the day of the month built.
If you want to save yourself opening up the axle, try to bring the original stamped info to view so you can know for sure what you have.
