I'm fixing a few issues on a friend's 1966 Mustang coupe, six cylinder. I know from the engine casting code that the engine is from a 1968 Falcon. No big deal, but the timing on a '68 is 6 degrees BTDC, and that on a '66 is 12 degrees BTDC, according to my info. Where should I set It? If someone knows what difference came about in 68 to cause the change, it might be helpful.