Rear diff third member.

I'm sure I need one guy I bought it from notices driver side rear wheel bearing leaking bad.. went ahead and replaced it.. got a real bad humming noise after I topped off the fluid.. I called dealer an gave him all the numbers.. it's a 4.10 non locking rear end.. I'm going to hunt one down at the junk yards they have a few.. 67$ if u pull it yourself.. my question is how do i go about identifying the right rear end to pull it.. I know that if it's a locking rear that it would have a unit on the diff.. I don't on mines.. but.to make sure i get the right one.. how do i go about getting the right one..
Would it.help to use my codes on the door to match the ones on the junk yard truck doors..