This is how member DAVENC mounted his second muffler in the above reference.
If is a Magnaflow 7x14 piece. I will be using this idea when I change my exhaust system this Summer.

8131436-MF7x14onCuda.jpg (61 downloads)

1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)