This should be in the What-if forum, I think.
I doubt Namu would manage to be strong enough to change much. We'd see him in the RRA Saga when Goku goes to Roshi's Island, and he'd fight those goons with Roshi. He could not be embarassed by Mummy Man later, but he'd still lose.
In the 22nd Budokai, he'd take either Pamputto of Man Wolf's place and fight either Goku or Roshi. That would be a nice fight and a nice character, but he's not winning.
I don't see him making it to the finals of the 23rd Budokai, unless he trains with Karin. If he does, he'll just be a 4th wheel in the Kuririn/Tien/Yamcha fodder team for the rest of the series. At least he'd be stronger than Chaozu.