Compare almost anybody in 1960 to almost anybody today and the 1960s person would be "more conservative" because the issues that are so divisive today weren't even on the horizon back then. So it's not really meaningful to say that JFK 1960 was somehow "more conservative" than McCain 2008.
For what little it's worth, if JFK had lived longer I really don't believe that he'd somehow go against his state, his party, and his family by becoming a Republican or being especially conservative. Most likely he'd drift the way they did. And if Kennedy were still alive today, at 99, he wouldn't be much of anything politically.
And if Kennedy were still alive today, at 99, he wouldn’t be much of anything politically....Why not? Clinton and Carter are.