With goku's personality and determination to be the best, together with his incredible ability as a fighter (sure, he is a dumb ass and naive in most of the aspects of life, but he is a genious when comes to fight, just see him fighting piccolo at the 23 budokai for example) I see him becoming the strongest ninja ever. He would probably even invent a jujitsu which would resemble kamehame lol.
Naruto, well, as someone said, would probably die in chapter one lol. Anyway, with the right training he could have become strong, yet I doubt he could survive a fight against vegeta like goku did, or even come up with the idea of surpassing the super sayan level during the cell saga.