My father's WW2 ARP helmet and our gas masks were all junked. Should have kept them for the grand kids.
Mechta Minor took a home guard gas mask and helmet into school when they were doing WWII in history. Turns out they all had a go with the gas mask. Not sure the parents would have been too happy if they had known about the asbestos in the filter...
With regard to the tank/helmet authenticity issue; given how little the tank had sunk into the ground before reaching the helmet, I rather doubt a helmet could take 25 tons of tank without being flattened.