I know where a 70 ft hole is that a husband and wife team pulled 18 onion bottles out of. It has a 90 degree drop off cliff from 25 ft to 70 . It is also in a deep curve and the river as under cut the side wall and has basically made a small cave....needless to say I will not be diving it....I will leave the deeper depths and sketchy dives to others.....
While tempting, that dive certainly sounds dicey, thus I applaud your decision to give it a miss. I've been teaching the Rescue Diver specialty for many years and a principal part of my teaching philosophy involves educating divers to "self-rescue" through "preventative" thinking. The easiest incident to rectify is the incident that never happens!
DSD