The GOP has not been left-wing since WWI, but the centrist argument is also flawed. I'll tell you why: because many of those Southern Democrats were conservative Republicans at heart but cynically retained the one-party system because it simplified things. The best example of this is Allan Shivers. Once they enter the GOP, plus the Goldwater candidacy of 1964, the GOP will by definition be pushed to the right. Otherwise you end up with an American version of our BQ in the South if both parties reject them. That's 127 EV, so any presidential candidate will have to be blackmailed before getting the votes. See 1876 or 1968 (where HHH would have to make concessions to Dixiecrats).