Joe - Those stamped codes are also sometimes located more towards the top of the passenger side tube on some axles. Your last picture makes this look like a GM A-body 10-bolt.

Here's a great resource article on GM 10 bolt identification and upgrades. There are even charts with decoding info to help ID the axle. Charts are divided between 1970 and earlier and 1971 and later axles.

Let us know what you figure out. wink

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)