Actually, there is no way to tell if a USA built Chevelle was/is a true SS by any numbers anywhere on the car in the 1971 model year.
You have to have some form of documentation such as a build sheet, protect-to-plate.
The exception to the rule is if it was assembled in Canada.
Starting in 1971 you could get an SS Chevelle with a small block or a big block 402 or 454.
Go to Team Chevelle at
http://www.chevelles.com and go to the message board forums for anything you want to know about Chevelles
Oh, by the way, you could get an SS chevelle without stripes or without cowl induction hood.