You may want to have a look at
http://www.slantsix.org/ . Please not that is DOT ORG, not dot com. Lots of racers over there getting good performance from the slants. Be sure to check out the articles section and pay close attention to anything written by Doug Dutra if you like to go fast and keep it in one piece. Crank flex does not seem to be a big issue even with the late model cast cranks. Early 70's and older slants all had forged cranks.
Scott.
