This photo proves that theory wrong, at least to a degree. While masterpiece male ass would be harder to find in the 1960s, it wasn't nonexistent, as these fine lads demonstrate.
I have a sneaking suspicion that Rupert on the right knows this, in his natty university blazer and oh-so-proper manner. He couldn't row if his life depended on it, but he volunteered to be team manager and dog's body to be closer to those dashing, sexy, naked heterosexual male gods. That might be the reason why he has his hands rather too far into his rather too commodious pockets.