>>What is the best kit I can put in this?
The best kits are the ones you don't have to pay a core charge for. This will not be a cut down version of the stock output shaft. So you'll pay a little more for this kit but it's better quality.
, Advanced Adapters
, Tom Wood
all make quality SYE kits.
>>How hard are they to put in? Do I need any special tools?
They aren't that hard to put in really. There is a good write-up Here
on installing an Advanced Adapters SYE in the NP231.
>>If I wheel my jeep will the drive line fall out the way it is now?
Your current shaft shouldn't fall out now with shims and transfer case drop. Just keep an eye on your u-joints if you have vibes now. Actually old/bad u-joints could be part of your vibe problem if you haven't changed them before.
>>Now if I do buy a SYE kit can I take out the drop t/case kit?
Yes you can put the transfer case back up where it belongs.
>>Do I take out the rear shims?
Yes and No. Actually you need shims to point the differential pinion at the output on the transfer case. You might have replace your shims with a different size. You can get new center bolts to replace your current shims/bolts if this is needed.
Or you can cut and re-weld the spring perches to do this also instead of using shims. Either way will adjust the pinion angle to point at the output of the transfer case.
It's best to call up one of the manufactures for these kits and talk to them for a bit. They will tell you what you need to do to get all the correct angles, mesurements for new drive shaft and such.
Hope this helps...