Here you go. Sorry it's filthy, but I drive mine more than clean it.
It's 6.5" in total length. The clamp tube is indeed cut in the middle, the squeezed seam disappears in the photo.
Three holes drilled into the extension easily welds the three tabs on the cone.
I leave mine on all the time, the extension clears both the clamshell and the license plate.
I think another aspect to the noise reduction in both of our solutions, besides diffusing the sound waves, is gettin the exit a little further out from under the car which, I’m guessing, reduces reverberations off/inside the clamshell.