the tunnels are considerably smaller in South Vietnam than in South Korea as I have done both in my younger…ahem thinner days and there is no way you are wearing all that kit, whilst crawling through the tunnels.
I have a photo some place of an original tunnel entrance and I have a UK size 7 foot that I measured against the entrance, and my boot was longer than the hole in the ground, I did manage to enter the tunnel but getting out was harder and I scraped my back quit badly.