HELP! Rear End ID

I've been trying to identify this rear end. I would like to know what it came from and what the gear ratio on it is. Here's what I know. It's a 5on5 4.75 bolt pattern and it's a 10 bolt cover. Obviously it's a GM (***uming Chevy) Salisbury style rear. The second picture is of the rear side and shows the code ZA 11 14 where the bottom arrow is pointing and K43 where the top arrow is pointing.

The 3rd picture is of the front side and shows the arrow on the left hand side pointing to the code 3839390N and the arrow on the right hand side is pointing to code GM4.

I've been looking everywhere trying to identify it and finally decided to ask you guys for help. Can you help me identify it or steer me in the right direction. Any help would be greatly appreciated. Thanks!

 

5 on 5" or 5 on 4.75"?

ZA shows up as a 73-74 full size p***enger 2.73 posi rearend, the K 4 3 casting date could be Nov 4, 1973

if it's a full size car from then it would be 5" bolt pattern. Check the ratio, how many turns of the pinion make both axles turn one full turn each?

 

Oops! It's 5 on 4.75 and it takes 3 turns of the pinion to make both axles turn one full turn each.

 

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