Thanks for posting! Actually I figured your '71 was a later production version because of the reduced number of louvers on the trunk lid. Louvers were gone completely for '72.

I was alerted to an easy "tell" for 6 vs. 8-cylinder 71-73 Big cars, a left hand tailpipe on sixes only. Someone in our neighborhood bought a brand new 71 Biscayne with a 6 & 3-speed manual. I actually saw it coming home from the dealer and saw it for the next 4 years when it went in favor of a new 75 Caprice Classic sport sedan.
Because of the easy tell, I was able to spot the rare 6-cylinder cars. There weren't many 1971 models equipped as such around where I lived, but for some strange reason I remember about eight 1972 Biscayne-Bel Air sedans around that I had personally seen in Southern Ontario back in the day. They weren't taxis either.

For 1973 the sixes only came with a 3-speed manual. Bel Air in the U.S. and Canada, plus Biscayne in Canada-only. I had kept my eyes peeled since the 73s were introduced but only have ever seen one in person (a Biscayne back in 1976).

That first 71 Biscayne I saw early in 1971 looked exactly like the attachment link I'm adding to this post: