I just spent 2 days making a 64 rear axle fit a 65 because it had that big panhard bracket which I had to cut off. I can tell you for sure it's a 64 or older. The 64 housing also had WE stamped on it. The 65 had HC, both were 3.73's.

'65 C-10, 65 L-60, 65 C-80, 72 C-60 & and a bunch of old Chevy cars.
Never time to do it right, always time to do it over.