The effects of OLD gasoline in a classic car

Sea foam. Also a stabilizer. i use it in anything parked for any length of time.
guy had a corvette, put it in storage at my place, didnt do anything about the old gas,and blew engine the day he took it out of storage. It started detonating on the highway and that was the end of it.
There could be more to the failure,bad distributor, plugged jets in carb and so forth.