Alloy USA Differential Permanent Cable Lock Kit
Imstalled one of these on my 89 XJ recently. This is the permanent lock version, not the cable lock version.
Works, but mine had a few issues. 1, thread for larger plug was roughly cut, had to lubricate and run in/out a few times to fix. 2, shaft which passes thru hole in fork had slight flare on end which had to be sanded down to pass thru hole in fork. 3, several misc small parts are included, presumably for capping off vaccum lines, but no reference made to them in instructions.
Pics to follow.