don't know
 

So i was thinking about up grading my under carriage. such as new long arms and different things. But what if i upgrade thoughts (long arms say) would they be able to be used if i lifted by jeep higher or got bigger axels in the future. i don't want to dump new parts in it if i'll need to change them out in the future. i was thinking of also upgrading my Dana 35c to a Dana 44, which i've read i'd have to adjust my drive shaft. then if i lift it to a 6 inch lift instead of my current 3, would i have to change my drive shaft again. sorry for so many questions.

Upgrading "thoughts" will cost you nothing :smartass:

So you currently have long arms, and want to upgrade to other long arms? Or do you have control arms going to the factory positions on the 'frame,' and just want better ones? If you already have long arms, you should keep the bushings in good shape until you lift higher, then get appropriate length arms at that time. If they have a lot of adjustability, such as they are almost all the way screwed in now, and you could afford a couple inches of unscrewing, then they may work - just make sure you always have at least 1 to 1.5" thread engagement-ish. If you have short arms, definitely wait for the lift.
As for the driveshaft, do the lift and D44 at the same time, if at all possible. If you do them separately, then you may indeed need to lengthen the driveshaft twice. Although if there is plenty of available slip in the joint without getting too far out there, the lift may not effect it. More importantly, if you are still running a slip yoke on the Tcase, lifting it higher will make changing that a little more important. You could get away with dropping the t case a bit, but it would be a band-aid.