BTW, your problem isn't the spring under and ubolts. It's the little bitty 31's. Going spring over will do nothing if you stay with 31's. Grind the tips off the ubolts and get ubolt skids if they are that big of a problem. My CJ5 on 35s and spring under goes almost as many places as my spring over CJ on 38's goes.
CSP has said it best! The only way to provide more clearance under the CJ (or any Jeep) is to go with taller tires. The amount of modifications and expense is directly related to the tire height you select.
bouts,it's my opinion that SOA isn't a solution for every CJ & YJ . . . I'm satisfied with my setup, but it's not the only way to build a good trail rig. Not every four wheeler is going to need to do the CA's Hammers, or CO's Independence & Die Trying extreme trails. Jeepwire had a great article, perhaps 1-1/2 to 2 years ago, where someone was discussing how to build a "killer spring under YJ."
If simply knowing how to weld was the only requirement to building a safe capable trail rig, there would be a lot of after-market companies and 4x4 shops out of business. My favorite post on another site is about a young guy who bought into the popular myth that anyone, regardless of skill level, can quickly learn what is necessary to do a spring over on a YJ. He apparently followed what he was told by friends and what he learned on the internet site and completed his buildup. He reported that he eagerly jumped into his "new jeep" and drove only the length of his driveway b/c of the vibrations, gear grinding, and noise coming from his jeep!
We generally under-estimate the value of a good experienced 4x4 mechanic; the problem is finding this qualified mechanic. It's one thing to install a rear tail-light assembly, switch out a battery, or change the serpetine fan belt on the YJ; it was quite another project to set up the steering geometry, or resolve the proper tilt to the T60R to avoid the rear driveshaft vibration at highway speeds when setting-up the SOA on my YJ!
It wasn't many years ago that 33" tires were the "big" tires in the after-market for Jeeps. With 33" tires and a 4" lift kit on the YJ, we were doing some pretty difficult trails in Colorado: 21-Road, Holy Cross, Mt Blanca, just to name some difficult trails we ran. 33's and 4" seemed to be just the ticket for most trails, even some of the trails in Moab, such as: Prichet Canyon, Hell's Revenge, Steel Masher, and Behind the rocks. Yeah, we sometimes rub the belly pan on some rocks, but we had a good time, no major repairs or expenses. Having had the pleasure of running the Rubicon, except for the "little sluice", the trail could easily have been done with 33" tires (however, I ran it with 35's).