The Wikipedia article on John Paul Stapp says he has the record, 46 g, but maybe that’s just the record for facing forward? The question arises looking at Aviation Week 2 June 1958 p23, which says “an Air Force captain” survived 83 g, facing rearward. Which is 60 mph to zero in 1.5 feet.
Page 15 of the 3 January 1955 issue tells about the Holloman rocket sled: it says the track was 3500 ft long and Stapp accelerated to 632 mph in five seconds, 2800 feet, then coasted for half a second, then stopped in 1.4 seconds. Those figures don’t add up, which maybe is why the claimed 35-g maximum wasn’t the maximum.
(Stapp had dealings with chimpanzees. Mary Roach quoted him: “If chimpanzees could talk, we would soon wish they wouldn’t.”)