For starters, other than fleet cars or special paint cars there were no COPO (Chevelles) in 1970, certainly not drivetrain related. Someone correct me if I am wrong. As far as the car in question, find out which plant and build date the car was made. 454's were not available till mid year so if it is an early car that would pretty much kill the chances of it being a 454. The rest of the drivetrain is also unique to the 454 so if the transmission, driveshaft and rearend are not 454 related that would be another red flag.
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