Case was much more progressive on Civil Rights to begin with, and very dovish on Vietnam by the late 60s.
I’d think that if Case was very dovish it might have lost Nixon states – including electoral-vote-rich ones – which he actually won by relatively small margins, for example Florida and perhaps California and Alaska. Then, would Minnesota, Michigan and West Virginia, which Kennedy won by relatively small margins, have not supported a dovish candidate very strongly?
This map – based on what has been said – would give Kennedy a win with 272 to 257 electoral votes, or leave him with 266 if Alabama was split as observed: