Any sagging will not be fatigued torsion bars. Could be upper and lower control arm joints/ball joints, control arm shaft and bushings or just torsion bars need adjustment. It all depends on what you mean by sagging and if it is really "sagging". Full inspection, with wheels off the ground, is necessary to discover loose/worn components. As far as disassembly of suspension, I would say no. If you are going to replace parts, they will be new. If there are areas that are missed by blasting, just wire wheel in that area. Also logistics need to be considered. If you need to move chassis around on it's wheels, then you can't take it apart. Also, do not take anything apart before you have the new part. So as to be sure you can get the part and to see how it goes back together as you do one side at a time.
Many front end parts available at Classic Parts of America. see 60-66/chassis and steering/chassis. Forget Ecklers, your truck is too new. Front end parts are available at Classic and FLAPS. You are in for some really, really expensive parts, so be sure you need them.
Be careful what and where you sandblast. If you are really using sand you can damage bearings and other moving parts. Sand will get into real tight places. Wheel bearings, differential bearings, bushings, ujoints, ball joints.........you are forcing high pressured sand into small cracks.
