Sealing the distributor is the biggie, Ive had water slosh half way up the windshield on my brat without sucking water, but the steam F's up the distributor about 100 yds later. A snokel is a must if your gonna get serious.
A surgical glove can be duct taped around the dist run the wires through a finger.
Also, water inside the coil wire ends will cause sum trouble.
NEVER! SHUT OFF THE ENGINE! with the exhaust pipe under-water.
Always service ALL the fluids and housings after a nice swim. It will save you alot of trouble in the end.
Venting all the housings inside the vehical is a good Idea.
Also when crossing a flooded stream in my 78 wagon I floated about 5 yards down stream. It was uncomfortable. But in bigger water it could be deadly,
use yer head and have fun.