I think we need a picture from behind of the fully finished exhaust (black with the protective mesh installed).
It appears that the exhaust gas from the two engine banks is kept separate (not mixed). This will make it sound more like two 4-cylinder cars.

If you want it louder then skip the mufflers. In that case I would use the US mixer box with tips and keep the exhaust gas path from each bank about the same length before being mixed. This would make it sound more like a (European) V8.

Laust