Why a ZJ instead of another XJ?
I would assume you could buy a stock Xj with a bad motor/tranny for dirt cheap ($200-300 range) any day of the week & swap over to it.
For that matter, you could probably find a ZJ witha bad motor & swap over in that same price range.
I woudl also assume it would also be pretty hard to get an insurance company to cover you for property theft if it was stolen from your yard or if you were injured while offroading.
here is an example:
http://cincinnati.craigslist.org/cto/1465958058.html