As for the L-72 I have read it was suppose to happen but never did no car has ever been found or paper work to support it. There was a Tripower set up that was also going to be available and when the vette boys heard about it they put the kabash on it .. They only wanted tripowers on there precious corvette .. The engine is in the build manual with a cancelled stamp on it .. it did not denote as L-72 I believe it was L-68 I found this.
http://www.impalass427.com/72res/67cancelled_3.jpg
http://www.impalass427.com/72res/67cancelled_2.jpg
http://www.impalass427.com/72res/67cancelled.jpg