I wonder if a Tremec 6060 could be substituted for a ZF-6.
The torque rating on the 6060 is just 50 ft-lb less than the ZF6-650.
I'm talking 4x2
I'd lose the granny and gain a super-tall top overdrive.
2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Rugged Air Dam