engine castings

I AM LOOKING FOR CONFIRMATION OF AN ARTICLE THAT I CAME ACROSS ON THE INTERNET. IT INDICATED THAT GM WAS EXPERIMENTING WITH THE COMPOSITION OF THEIR BLOCK CASTINGS IN THE LATE 60"S AND EARLY 70'S. THE ARTICLE POINTED OUT THAT ADDITIONAL TIN AND NICKEL WERE ADDED AND A STAMPING WAS INCLUDED UNDER THE TIMING CHAIN COVER . THE STAMPING READ 010 OR 020 WHICH REPRESENTED THE % OF ADDITIONAL TIN OR NICKEL THAT WAS ADDED. THE ARTICLE INDICATED THAT THESE BLOCKS DISIPATE HEAT BETTER. IS THIS CORRECT ??