The 68 and 69 Chevelle are a lot alike. But for me, the differences that separate the two are the taillights. The 68 has thin, sideways rectangular taillights while the 69 has more of a vertical, block, rectangular like taillights. The 68 model also has a vent window.
The 70, 71 and 72 are a lot alike. Although the 70 has dual headlights and sideways rectangular taillights. Both the 71 and 72 models have single headlights and round taillights. The 71 and 72 are too much alike for me to tell the differences. I doubt I could distinguish between the two if sitting side by side. I will takes TerryP's word that is a 71 model. That is a beautiful, slick car and sounds right.
I have been told that the headlight and taillight blocks can be swapped out between the 70, 71 and 72. It doesn't change the model but just changes the look from one model to the other.
I am not certain on this but I believe a number of engine sizes and trim packages could be ordered on the SS Chevelle and Malibu. The gas crunch started around 71,72? Muscle cars of that era started to become much more tame, gas efficient.