Remember that the pinion spins X times faster than the tires due to the gearset in the diff. Those rotors will get very, very hot.
You'll have to find a way to let the heat out of the rotor, rather than let it seep up and down the driveline. I've seen countless seals go on pinions and ujoint caps.
Cross drilled and slotted rotors might be the way to go.
Might be worthwhile to try and convert to hydraulic disc brakes, and save the pinion brake for an e-brake/parking brake. Look at Willwood for the calipers and rotors and bracketry to go on the Diff. Then there is also USA6x6 (if you are willing to wait for a long delivery time).
Or keep the air-brake setup? Not sure if you would need a Class1 or air-brake endorsement for an OHV application.
Good luck with that, let us know how it turns out!