This is absolutely false. There are many Republicans who are openly and unabashedly pro-abortion. In fact, before Roe v. Wade, abortion was first legalized at the state level under the influence of Republican governors -- Nelson Rockefeller in New York, and Ronald Reagan (yes, Ronald Reagan) in California.
The GOP is only considered a "pro-life" party today because it is now dominant in parts of the country that used to elect conservative Democrats.
Not absolutely false! Take a re-read of the platform statements of both parties. What party is it that consistently approves of all abortions now? Is it the Republican Party? NO! You mentioned the govs of two Blue states (with heavy RAT participation among voters), including Reagan, but they were not the leaders of the Party.