Ron Paul won't be the R candidate because he barely fits under the R tag as it is. He isn't as bought and sold as the other candies so he doesn't have a chance what so ever. I'd simply vote for him to see if his crazy ass would actually do anything different.
He'd send a balanced budget to Congress, and would order all troops home the day he took office. As for whether he's a true Republican it kind of depends upon what your definition of the Republican party is. He's a Robert A Taft Republican, but not a Lincoln, Rockefeller, or Reagan Republican.
The modern Republican Party was initially the Party of Lincoln based upon the Whig Party of Clay and the Federalist Party of Hamilton, then in the interwar era, it had two competing, almost equally dominant factions. The Eastern Establishment (led by the Rockefeller Republicans) and then the Robert A Taft Faction. The Robert A Taft faction is what Ron Paul fits under. However, it has returned to its Lincolnite roots (except for protectionism). Still, I like to think of the Republican Party as the Party of Robert A Taft and the Democratic Party as the Party of Wilson, because Wilson was the first modern Democrat, and Robert A Taft was the opposite.
As for the Nolan Chart, while there have been Presidents who were pure statist and others who were close to Pure Libertarian, there have been no pure lefitsts nor rightists. Reagan was liberal economically and not 100% conservative socially.
The closest to the left-end and right-end of the Nolan Chart are probably Hoover and Polk, respectively. However, those two both held opposite positions on alcohol, and Polk created the dept of the interior and Hoover presided over the first Mexican Repatriation.