[W]hen looking at the dynamics of a presidential primary, candidate history can only go so far. More important are the party constituencies and interests that shape the dynamics and incentives of a nominating contest. As governor of Minnesota, Pawlenty built a moderate image and governed from the center-right, but as a Republican candidate for president, Pawlenty will adjust to the issue priorities of the conservative coalition. And if he wins the nomination and the presidency, those priorities -- as well as his own issue emphases --- will be the best guide to his actions.That's exactly correct.
The current fight for the GOP nomination has very little in common with, say, the fights in the 1940s and 1950s between the Eastern Establishment of the party and the conservatives. That fight basically ended for good in 1980. There are different groups and interests within the party, and sometimes there are fault lines that force politicians to choose between them, but whoever gets nominated is going to be basically responding to the same groups. The remaining questions are more about strategy and tactics than they are about either basic philosophy or which interests will be represented by a Republican White House.
The one place I could imagine a real difference between candidates would be on foreign policy; there are serious rifts between (warning: shorthand, overly simplistic names) realists and idealists, with substantial policy implications at stake. However, I very much doubt that we'll see that seriously debated in the GOP primaries. It's much more likely that instead we'll see candidates competing for who can mouth the toughest-sounding cliches, while muddling through on actual policy.
Beyond that, you can expect lots of attempts by candidates who basically occupy the same space to differentiate themselves without moving at all out of that space. So: not about, say, who is for cutting spending, but lots of symbolic stuff to show that a candidate is most for cutting spending.