The revisionist history is claiming MLK was a Republican.  His father was (as were the vast majority of African Americans in that era).  MLK never identified with a party, however he did campaign on behalf of LBJ.  

Putting aside for a moment the absolute lack of logic in your argument (Democrats were racist in the 1860s, so Republicans can't be racist now!), you are ignoring all history after 1960.  Seriously.  Read up on Nixon's "southern strategy."  Johnson's push for the Civil Rights Act alienated the racist wing of the Democratic party, which briefly formed it's own party before flocking to the GOP in the 1970s.  Those are facts.  Regardless of whether or not you believe them.