I just watched part 3 while having a morning tea break. Unfortunately you can't see any footage of the 4th vehicle crossingThe John Canny video of his trip to Cape York (Part 1) shows you part of the PDR:
View: https://youtu.be/a3bP6ur6A-M?t=1948
The first three have snorkels/RAI's and it looks pretty deep.
Unfortunately no footage of the 4th vehicle was taken.
It would have been interesting to see how a vehicle with no snorkel or RAI handled water this deep.
The video just cuts to a splash screen with a simple large statement with an !!!!!!