yeah, the pic they used looks like a grenaded flywheel and I doubt too many 4.0s could get that much rpm. :)
here's a peugeot rebuild kit for anyone that needs it:
chances are that you just need the existing carb adjusted. just gotta find a local shop that specializes. carbs are really hard to diagnose over the internet. :(
this is probably not the right advice (I don't know carbs), but many moons ago with my old 86 I adjusted the idle screw to bump up the rpms. :) (it's a little set screw that the throttle arm rests against at idle)
2dr and 4dr XJs share the same flat floor, so their floor brackets are very different than MJs. you'll need to mount the XJ sliders on the MJ floor brackets. pretty easy to do.
but 2-dr XJ buckets do lean forward like MJ buckets (4dr do not), which makes them more desirable for us. :)
yeah, I regret not being able to keep mine when I sold my 86. :( plus I guess I don't really need a collection of axles. lol.
my new favorite rear axle suggestion is the Liberty 8.25 as my '06 is a couple inches wider than an MJ stock axle (to better match the wide MJ bed) and can be had with factory disks. plus KJs are super plentiful in the junkyards.
If I was starting over, I'd swap in a non-MJ prop valve up front (XJ, WJ, etc) and then an adjustable one for the rear line. Seems that gives you the best chance at dialing it in juuuust right. :)