Got trans unwrapped and started measuring everything up. I mocked up a nv4500 adapter plate and clutch.
Everthing bolts up with exception of the clutch disc. The NV4500 uses a 12x1.25 disc whereas the G56 uses a 13x1.375 disc. The G56 input shaft is larger and the spline engagement sits approximately .75 inch deeper into the bell.
This left me with a few options:
1. Since I have been unable to cross reference a stock application 12x1.375 disc I would be looking at a custom disc. Even then I'm not sure it would have enough spline engagement.
2. Upgrade to a 13 inch flywheel from a NV5600 equipped truck. That would require a starter spacer adapter. Then use a 5600 clutch.
3. Use all stock G56 clutch components with a dual mass flywheel. This would require no spacer, but the dual mass is not the way to go.
So after all that, I called Greg at Southbend (over several calls) and his opinion is that I should use an aftermarket single mass G56 13 inch flywheel with my stock nv4500 adapter and starter. Then use a nv5600 spec clutch kit. This gives me the best of both worlds and does not require a starter spacer. Plus it gives me the correct engagement and depth. Instead of trying to piece together the stock pieces, I just ordered the Southbend kit, knowing if I blew the clutch in the middle of nowhere I could replace it with a nv5600 unit. Plus the Southbend single 5600 kit is rated to tow over 20,000 lbs. regularly.