Replacing the shocks will not increase the ground clearance. It will, of course, improve the ride and handling if the existing shocks are not good or not in good shape. Similarly, a rear stabilizer bar won't increase the ground clearance.
I would take the rig to a reputable spring and chassis shop (one that deals with trucks, etc.) and listen carefully to what they recommend. It may well be that simply repairing or replacing/upgrading the rear springs will help a lot. The rear end does appear to be riding low; possibly that's because of worn or broken springs, and possibly it's due to poor weight/balance as manufactured; both are entirely possible.
Note that the rear springs will (probably) not appear to be arched greatly on this chassis; they're nearly straight, albeit mounted at an angle.