Ok, I'm thinking you mean the Jimmy Ellis that lost to Frazier, Kirkman and Shavers Ali and Rubin Carter, but I thought you could have meant the one that actually fought in the same era who lost to Foreman and Briggs.
Either Way the Tua man gets the nod from me. If your talkin 60's Ellis he just didnt do well with power punchers. Tua is too big for him. I know he was a slick boxer but I still think Tua catches him or just overpowers him in the long haul. I see this playing out like the Lyle fight most likely.
The other Ellis never really did well with the upper crust talent.
Now if you put them both in the Ring against Tua at the same time. It gets closer.
Jimmy Ellis -- in his prime -- would have had no problems Tua. When Ellis moved up to the HW division in 1965 and until 1973, he lost only to Ali and Frazier, while beating Chuvalo, Bonavena, Patterson, Quarry and Leotis Martin. Quite a resume.
His other noted HW loses mentioned above occurred when Ellis was clearly past his prime and in the last 2 years of his career. He retired less than 2 years after the Shavers KO, and only 1 fight after his second loss to Frazier.
Ellis would easily outbox Tua. The Frazier comparison is awful, b.c Tua was much slower and didn't provide the constant fire that Joe did, or near it. Ellis would easily avoid his wild left hooks. You saw the Byrd and Nicholson fights (until the KO shot) Ellis hit harder then both those guys and would make Tua look like an amateur. Bonavena was basically an in-shape Tua with less power but better stamina and Ellis creamed him.
I think that the Tua that showed up and lost to Ike would get the job done with Ellis. He wasn't slow and he didnt tire. But I see my thoughtful and expert opinion is fast being subjegated to minority status.
Having thought about this one I edge towards Jimmy Ellis on points. The Ellis of 67-68 who beat Chuvalo, Quarry, Martin, Bonavena and Patterson(?) would kmow too much for the dangerous but one dimensional Tua.
Ellis WPTS12 or 15.
Although Tua would of course always have a punchers chance.