If Ali was born ten years earlier?

He would have died in 2006.

 

He still could have been drafted as Vietnam started in 1954 or 1955.

 

Rocky wasn't good for him style-wise. Tough fight to predict. But I think he would have won against Marciano and it would have given him great fame. Later, probably strong victories against Moore, Patterson, quite easy against Johanson, of course he could fall along the way and somewhere in 1960 Sonny Liston gets the fight of the century. They are both of similar age, Sonny is probably hungrier, in my opinion he would have won against Ali and Muhammad would have been in the top 10, but not in the top 2 like today.
However, it could happen that Muhammad would win against Rocky and Sonny and both victories would be very important for his legacy because Sonny gained a strong status as a contender, which does not happen often. He could be undefeated by Frazier. Then the chances for top 1 would be significant. But I think it's more likely to lose in one of the fights - Marciano 30%, Patterson 30%, Liston 50%