Can you ID my rear axle housing?

[chillware]

Hi guys,

I'm trying to figure out if my rear axle housing is stock for my truck or not. Here are the numbers I found on it.

On the left tube is 3838227 with the letter 'N' to the left and below that number. And on the right tube it says GM4.

It is a 12 bolt w/ 17 spline yoke and axles.

I think the gears are 3.73.

The truck is a 1966 C10 2WD.

Any info would be great, Google knows nothing about that number

Thank you!