If you want to unlock a welded rear, you'll need to replace the internals... ring and pinion gears, spider gears and carrier plus the install bearings and shims. Basically, a complete overhaul.
All CJs have leaf springs, I'm not really sure how that relates to anything. "bad ass" means different things to different folks, do you want a lifted Jeep with 33" or bigger mud tires? Steel bumpers with lights and a winch? Show Jeep with pristine body work and paint?
Depending how it was welded, all you will need is a carrier, spiders, cross pin, and roll pin.
But ive seen some pretty haggard Lincoln lockers where everything was compromised because of slag