Well, I'm far from an expert, but I do understand the basic theory in auto transmissions. To handle more torque, you can do two main things, raise the pressure of the fluid, and add more clutch packs.
As far as the fluid goes, some boxes you can raise the overall pressure, and everything follows suit and works fine, others you have to raise each individual drive section separately, because an overall change will mess with shifting, etc... I suspect that these will fall under that category
As for more clutch packs, its probably a matter of ripping one open and looking. The 722.6 packs might be the same dimensions except thinner, allowing room for more packs. Its going to be hard to determine without ripping one open and looking. There might be other internals that swap, but the clutch packs is going to be the biggie here.
PS I just read how old this thread is. Traffic is slow in the diesel performance section eh...
Well, my reasoning still stands...
PPS I just started reading through that other thread. So 3mm plates are available, and if ours came with 5mm stock, a little swapping should be possible.