I think 1960 - 1963 was too early, as he was young & hadn't filled out yet.

I think by 1966, he had filled out & he was in his absolute prime.

Arguably, his 'prime' years were the 3 years he spent in exile, but that's only speculation on my part.

The Ali that beat Cleveland Williams & Zora Foley was the best Ali we ever saw & arguably the finest HW ever.