My deuce came from the USMC with some deep fording kit items factory installed, like the low pressure regulator, "fording handle" on the dash, a check valve between the air tanks and the associated plumbing.
That made it easier fo me to complete the installation with store bought parts.
I wouldn't do anything to the transmission breather valve, it allows the pressure to build up when the bellhousing is pressurized. If you vent it, there will be no pressure build-up in the transmission and bellhousing.
For any fording operation is would be rare to have water in the cab anyway since a water crossing can be counted in seconds and with the doors closed, water could only enter through holes around foot pedals etc.
The crankcase filter is worth the $200 IMHO, I collect 1/10 of a quart of oil in the sump every 1,000 miles and permitting the filtered fumes to recycle via the air intake probably makes my deuce one of the most environmentally friendly trucks around (especially with bio power).
The compressor to air filter canister is 1" heater hose (that's one inch I.D.).