We have had very good luck with the Post '77 OEM 2/3F series distributors on the Cruisers with the O- ring, screw down cap and venting system. On the minis and the '93 and newer '80s you have to seal the vent holes in the distributor body and run vent lines instead of the short rubber vent/cap that is used from the factory. Personally for Chevy HEI distributors I drill and insert fittings to vent the distributor like the later 2 and 3f engines do and then seal the cap to the body of the distrbutor with silicon sealant
If you use silicon sealant, make sure that you use some weak stuff so that you can get the cap off again. Or... what I do is smear a little oil on the cap before setting it into the bead of sealant so that it does not stick.
The OEM plug wires on the FJ60s and later Cruisers fit very snug at both ends and are hard to beat. A liberal application of di-electric grease will do a lot to keep these connections sealed.
Any time you short out a plug in deep water, or get it in the distributor, it is simply a matter of drying off/out and it will work fine. The plug is not really fouled, the spark is just finding an easier route to ground.
It is a good idea to keep your ignitor dry too. On the EFI rigs with electronic control modules, you need to seal these also in case you swamp the rig or simply have a long deep crossing and wind up with water inside the rig. Silicon sealant around all the seams and liberal application of di-electric grease in/on all the plug connections has worked great for me and mine.
Make sure your snorkel is sealed well.
Keep your speed down so as to reduce/eliminate splashing that throws water hard against connections and components. Driving has a lot to do with it too. it is easy to jump in splashing and charging only to kill your engine from water blasting everything under the hood. Turing upstream is usually not a good idea. Failing to pick a good line for the crossing is the biggest reason for failure.
They shorter rigs that run with us often have distributors and spark plugs underwater.
Obviously a taller rig has an easier time in deep water than a shorter one.
Mark...