BIG rig,
Good thinking. This is what I did a few years ago. A friend gave me his surplus 3500 upper secondaries and I added them to the upper pack. Wanting to lift the rear up just a little more to make the truck level with the TC on, I added a single lift spring in the main pack so it now sports 8 leaves. Plenty of spring support now, plus a bit more travel, if you can believe that. Search back jefe4x4 to find pix and plans of the upgrade. You will probably need to get the longer U-bolts for the upgrade.
regards, as always, jefe
'01.5 Dodge 2500 4x4, CTD, Qcab, SB, NV5600, 241HD, 4.10's, Dana 70/TruTrac; Dana 80/ TruTrac, Spintec hub conversion, H.D. susp, 315/75R16's on 7.5" and 10" wide steel wheels, Vulcan big line, Warn M15K winch '98 Lance Lite 165s, 8' 6" X-cab, 200w Solar