With his physical strength, hand speed and low center of gravity, I wouldn't want to be lined up opposite him. He may have suggested lamenting his slowness of foot, but his athletic background also explains why he was so hard to move and knock off balance. Keeping low and reacting fast came naturally to him.
I read a reprint of it myself during the early 1980s, probably in KO Magazine. A quick on-line check failed to turn up a direct link (or even a reference to it) immediately, but we know Frazier-Bonavena I occurred on September 21, 1966. So at least we have a time frame for the original publication. (Later, I'll look through the stack of old magazines I have close at hand, but can't promise I'll find it among them. I don't know if he was still writing for the New York Journal-American, or had switched to the Hearst owned King Features Syndicate by this time. Probably the latter, this late in 1966.)
February 1971, Joe Frazier did train at the Concord Hotel, in Sullivan County. And very quietly, as he did his morning runs by himself, with no fanfare.