I will be interested in hearing his exhaust note and comparing.
I notice the routing for the pipes is different for the left and right pipes. I am guessing this is because of the diff and other bits. My fabricator faced the same issue but managed to get symmetry by creating a smaller back box with 1 in 2 out for the pipes.
This gives a visually more harmonious exhaust pipe routing. Possibly freer flowing and better sounding but not sure about that bit. It also gives lots of room to split the pipes from singles to doubles each side.
Just a thought in case you wanted to suggest it to Matt