What rear end to buy?

Locker???? Don't know where you got that information

Exploded View - Inside the Eaton TrueTrac Differential - YouTube


You posted the link that you apparently didn't read, see above i highlighted the part where it says locker in red...

I only clarified what you linked, it does have the A in the part #, but they have it as locker, usually the lockers are S, pointing out the description