You asked for old timers. Do you rate mitt work as necessary ? I think lots of great fighters never ever did that. It's only been really fashionable in the last 20 or 30 years, from what I can gather.
From an old thread, the much-respected, now deceased, John Garfield (Joe Rein) wrote this : Or are pads different to "mitt work" ??
Old timers hit a heavy bag, a speed bag, and a double ended bag. Mitt work, I think not, but they did shadow box if that counts. With limited or no video, the sparring partners were more important.
Old timers also fought a lot .. Willard is a very unusual case .. the man did not even take up the sport at all until his very late 20's .. to accomplish what he did I feel was amazing .. if he actually started out with some sort of amateur career in his teens and was built up I think he would have been a hell of a difficult fighter for sure ..