Personally, I don't know why some people go to all the trouble sometimes.
I've forded streams with water half way up the windscreen with lift kit, 14's, but no tube extensions for diff or gearbox (maybe that's why the centre diff went in the box though

If you can create the right bow wave & if possible have the left side of the car (the distributor side) downsteam, then you can go pretty deep.
Ron was a pretty cautious guy but kept his cars in good nick though too.
And whatever you do, DO NOT seal up the timing belt covers. You'll simply overheat them. Water can't get from them into the motor unless your seals are stuffed.