[Paul D]

Here's a pic of the exhaust exit and a better view of the gas tank. I believe it's just unpainted steel with 40 years of patina.

Yes, the exhaust has been replaced with stainless steel pipes and mufflers. I understand that L78 Chevelles as well as L72 big cars did not have rear resonators, and therefore the exhaust exited right behind the rear wheels. Although I may have missunderstood your point on long vs. short exits, I assume mine is and was the "short" exit. I know on big cars a way to help determine whether it was an original L72 is the unique location of exhaust pipe hanger mounting holes in the frame. I assume that's the case with Chevelles and L78 also. Is that correct?