As much as I love Jersey Joe, I can't see him doing particularly well here . Maybe Walcott can outbox him the first few rounds, but once Frazier starts smoking, he's in deep trouble.
I think this is about styles. I'll go with Joe, but I've always believed that Walcott would have beaten Ali. He was smarter and fitter than Young and he packed a KO punch. Frazier, though, would have overwhelmed him, IMO.
Not to argue your choice of Joe over Ali here but the comparison to Young doesn't gel as it was a older ice cream eating Ali that Jimmy fought, the prime Ali would have dropped and stopped Young.
Tough long fight but I think Frazier comes off the canvas to stop Walcott late in the fight. He would just grind Jersey Joe down and his body attack would be a major factor.