When I was a kid we used to think that the 396 was the hot setup and that the 402 was a dog. Not sure why, that was just the "word on the street" back then. But really if they both were built with the same parts then they should run just the same. The L98 402 was pretty stout with 375 hp rating. I'm not sure on the '69 and '70 thing. Officially the SS 396 was actually a 402 in 1970 but it wouldn't surprise me at all to find out that some of the '69 cars got 402 engines. The factory wouldn't care that much about that stuff. They just put them together with the parts they have on hand.