Where the confusion comes into this is that Socialism is split into a left and a right wing. The right is Facism(Bolshevik), the left Communism(Menshoviks). That is how Hitler came from the right wing. Do you have any references to the use of the terms right and left from that time period? I always thought in these inter party battles, the winners called the losers 'counter revolutionaries." I never saw anything that used the terms right vs left.
Lenin(a Marxist-centrist) always refered to the "Communist Left" and called the "Fascist right"(among other things like "a filthy rabble of former pro-Austrian nationalists, freemasons, republicans, mussolinists and other dregs of the socialist movement".) Of course he had choice words for the "Communist Left" also(infantile disorder, renegades, liberals, etc.)
As for a source, just google it with socialism, communism, fascism, left and right as your search terms, I'm sure you'll get lots of hits.