Not sure if that's the right one. It says install in open diffs only? If your rear end originally had a posi, it'll be on that sticker, should be G80, which is for POSITRACTION, LIMITED SLIP. I believe this is the code for the newer limited slip axles, that arent true posi's. G76 is for the positraction code, I think this means the old ones.
Look for the G80 then, and because it's very useful for decoding your RPO code sheet;
http://www.c2e.info/rpocodes/
As for the aftermarket carriers, I'm not sure. I don't know if the one you got will work. I'd look around on Summit and Jegs, see what you think.