I would guess the sound has a lot to do with the engine as well. I've heard a 3800 (supercharged) come very close (I couldn't tell the difference between the wav files) to the right sound since it is also a high-revving motor. The downnside of engines like the small block chevy is that you hear the distinct V8 warble. But to answer your question, I've seen a few pics of people trying to get the right sound by making cutom headers. There are also other mufflers that let you adjust the pitch of the sound. I have't heard of anyone using the ******* mufflers, but I'm sure they're out there.
--------------
my site http://www.statikdesign.com/scratchbuilt/