What is it about the CRD's that they cant use most of the lift kits out there?

I looked at rough country - no diesel, daystar - some diesel. Are the coils different for putting in pucks?

Or is it something else like brake lines in the way or something?

The springs have a higher rate, the front diff is moved over a bit so you cant lift them over 2.5" or so. But the actual suspension parts are the same, keep it under 2.5" of "real lift" and its very doable and has been done many times before. Ypu can go 4 inches on the CRD but it get way more expensive than a gasser becuase the diff moved over, gotta get cut cv shafts from JBA.

Plus spacer lifts suck on a KJ. Do OME CRD springs and be done forever. Rough country, Rustys, Daystar all make sorry excuses for a KJ lift.

Please read the lift faq

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2002 KJ Limited 3.7, 5.25" lift via coilovers, custom HD rear springs, 32.2" tires on moabs (soon 33s) 4.56/JBA diff, OX lockers front/rear, NP241OR, Parker Fab front/rear bumpers, rock rails and roof rack, Viair OBA.

2006 KJ sport 3.7, 4" Ironman lift, 32" tires, Parker Fab front/rear bumpers and rock rails.

You're looking at cheap spacer lifts that are well cheap and don't work.
Plenty of lifts out there if you lift one right
You have OME full spring lifts and Ironman full spring
Plus you have a adjustable coilover lift from jeepinbyal , also OME and Ironman are available from him as well
Also from ALLJs ( boulderbars.com) you have the Frankenlift of which they make one for the CRD

Everything is the same between gas and CRDs except for heavier springs for the CRD ( stock they have 410 lb springs most go to the OME springs which are 500 lb rating)
OME full spring kit that comes with shocks is great with an CRD

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MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited