The idea of the purity test itself is pretty laughable. Big tent?  As one pundit put it. Yea conservatives have a tent.. its pretty much empty with everyone crowded over into the the far right corner.

They have alienated moderates  independents  latinos  blacks  pretty much everyone but old white men.

They are busy separating the wheat from the chaff  alright.

A conservative believes nothing should be done for the first time

More than negotiated, actually.  And, as you mentioned, DOMA wasn't on his plate, but while governor of California he was instrumental in helping defeat 1978's Prop 6 (The John Briggs Initiatve), which would have forced all gays out of the California public school system.

I have spoken before about the fact that virtually no Republican in the 20th Century would be welcomed by the current Conservative Taliban Movement as "one of their own", unless they shifted dramatically to the Right in accordance with today's demands (a la Mitt Romney's Right-wing lurch).  Nixon, Eisnehower, George H. W. Bush, Goldwater, Coolidge--none would come even close.  If Reagan would be seen as "not Conservative enough" in the labyrinth of lies and extremism and delusion which is now the Right, there is only one 20th Century politician I can think of that _might_ still be in their camp;  Joe McCarthy.

And, BTW, by 2016, George W. Bush will have been so thoroughly painted by the Right as a weak Liberal Pinko that whatever tenuous strains he currently still has with the Conservative Taliban Party will long be severed.  This process is already underway now.