The resonator that you've got the image of I thought only had "export" applications and wouldn't have been found on domestic cars with the exception being a '92 - '93 LT1 car. It seems that the resonator had applications for those years.
I would have expected this:
but was later serviced with this:
and that's what I believe is on the others that mentioned there was something there.
Here's a link to an image that pretty much explains my thought but I didn't base it on this:
http://parts.nalleygmc.com/showAssem...ssembly=403928