I have heard both engines in person with the 180* exhaust, and they sound identical except for the sound of the SC on the 3800.
It seems to me the money to do this exhaust could be better spent elsewhere on the build though. Yes, there is a difference in sound with the 180*, but it is still nowhere near the sound of an actual V-12, and basically sounds like a V6 with tuned exhaust.
The sound a V-12 makes is derived from the stroke of the engine, no header or putting an OEM Lambo exhaust on will make any difference in the sound.
I have heard a 60* V6 with all stainless steel exhaust, and that sounded even better than the 180* set-up.
Also, keep in mind that Lambo engines are from Italy, and the 3800 is from America. I think the first difference between the two is the accent of the mice inside them.