Not 100% sure but I believe the ARB is the only available locker unless you want to swap gen II/III parts in.

Gen II's have an LP air actuated locker stock from the factory but different sized diff than the gen I.

Gen III's have an LSD that's supposedly modifyable with a few parts to make it a locker but I don't know if anyones even seriously considered putting one in a Gen I.

IMHO, unless you're really going hard core (beyond the difficulty of the Rubicon) and/or simply don't have enough articulation then you're a likely canditate for needing a Locker. Otherwise, you can likely get buy with a properly functioning LSD and it's safer on the street. FWIW I've personally done the 'con w/ only a rear LSD.

Of course getting a locker just so you can say you have one is a whole different story. <img src="/forums/images/graemlins/smile.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />