Rear brake setup with parking brake cables would be best. Either foot lever on left side for setting or hand lever adapted to bolt onto your transmission. Borrow parts from another model AD truck that had this setup, and the parking brake cross shaft behind the cab.
If you're good ad swapping stuff around you may find that you can adapt drum brakes from a somewhat newer model 14 bolt axle, these have parking brake cables.
Some reading here. Though I have not fully investigated adapting the newer drum brakes on the old Eaton I'm reasonably sure it can be done one way or another, and it might be real easy...
https://www.stovebolt.com/ubbthread.../14-bolt-axle-swap-info.html#Post1249600
