I agree a snorkel kit would be neat.
When I had my Bronco with the 4bt, I found out that the engine wouldn't get water in through the vent unless you cut the engine off. It sucks water in quick when it is cooling down. The vent and the air intake need to be as high as your head in the cab. You're not going to be driving in water any deeper than that. The next thing to look out for is your fuel cap. If it is under water for more than a few minutes you will get water in the tank.
You will get water in your transmission, transfer case and differentials no matter how high you raise the vents. The seals on these are primarily designed to keep oil in and dust out. Water will get in.
If you really want to get serious you could adapt a deep water fording kit from a HMMWV. It actually equalizes the pressure between the water and the inside of the differentials and the transmission by putting a small amount of pressure on the vents. It is pretty effective at keeping water out as long as the engine is running.