[Late BrakeU2]

I know prior to 1970 GM had a restriction stating no mid size car engine could have a displacement larger than 400 c.i.(hello COPO)but that was dropped the following year.A marketing standpoint and insurance are the only plausible reasons-Camaros and Novas were entry level where as the Impala,Chevelle,Monte,(Firebird,GTO,Buicks) targeted the "older" buying influence who were much less affected by insurance due to age.On a side note I think that's why so many more of the latter have more docs-the people that bought them were generally older and knew the importance of keeping records jmo