351w flywheel

the difference is the diameter of the flywheel mostly. the larger flywheel allows a larger clutch disc to be used for better grip. you do need to size the bellhousing to the flywheel as starter location does change. you cannot use a 164 tooth bellhousing with a 157 tooth flywheel, or vice versa. one way the starter will not engauge the teeth, the other way the start gear jams against the flywheel.