This is one of the few scenarios I could possibly see JFK losing because he wasn’t as known as he was in 1960 obviously. However at the time a majority of the country was Leaning Democratic. It would be a true tossup. IKE was extremely popular but Nixon was not and there was even talk that he left off the ticket in ‘56. I’ll give the nod to JFK because I’m bias to JFK for one and for two he is a brilliant campaigner and if they had Debates - I think he uses them to his advantage the way he did in ‘60.
JFK keeps the South solid Democratic, wins the Northeast/Mid-Atlantic including PA & NY.
JFK holds off Nixon, winning 274 EV.