I tore the motor down gen 6 502 edel. alum. heads etc. Anyway the knock I heard was a piston starting to sieze. The skirt is scratched to hell as well as the cylinder wall (#3/and #5).My machinest feels that there was a lack of water to the cyclinders.He also found all 4 valves in these chamber mushroomed (over heated) and the head slightly warped.We are thinking I may have ran the wrong head gasket.The head gasket combustion ring also shows heat marks around the same two cylinders.I am running a holley hp 950 by bigs primaries are 80 and secondaries are 86/wiend tunnel ram/msd ign./The carb should have been set up to my specs turning 6000/ the only thing I did kinda strange is turn the scoop foward no air cleaner /machinest said he doesnt think this is the problem. Any Ideas? sorry so long!