Pros and cons to lifting by underslinging my axle. What all else needs modified?  

On a CJ using the CJ springs? Bad plan. But with YJ springs and maybe a torque arm to control axle wrap, that would be a good lift plan.  

Here's the problem, if done correctly it will take more time, money and resources than simply buying and bolting on a lift kit. If you think you want to do a spring-over because you think it's less expensive, don't bother. By the time you have completed a cross-over steering conversion, replaced driveshafts, installed a rear traction bar, and dealt with leaf spring failure it will cost several times more than a simple bolt-on lift kit. Now, it you simply want the performance and compliant suspension provided by a spring-over and cost is not a major issue there are a couple ways to do it. I highly recommend building a four-link for the back end and then double shackle mount the rear leaf springs. Don't bother with the CJ stuff. Go for some stock '87-'95 Wrangler leaf packs. This way you'll get the predicability of leafs with the flex of a four-link. Up front, go with the same Wrangler rear pack or a Rancho PN 44044 leaf spring. Use a crossover arm, new brake lines, shocks, driveshafts and so on. Of course all of this requires extensive fabrication skill.  

a nice high cross over steering is about 450 bucks,.... also a big advantage if ya plan to get a highsteer any how.

cross over steering