Anybody ever see a N97 Noise Reduction Package on a slant six Duster?

Hi All: My 1974 Duster with the 225 six engine has the N97 coding on the broadcast sheet and fender tag. My understanding is that this the "noise reduction package", which is a resonator added to the tailpipe. I believe that the resonator was part of a larger overall package, called the "Deluxe Sound Insulation" package which automatically came with the Gold Duster package. Page 11-2 of the 1974 factory service manual clearly shows that the 198 and 225 six cylinder engines could come with a resonator in the tailpipe. Does anyone have a 1974 dealer ordering manual which describes the contents of the "Deluxe Sound Insulation Package"? Has anyone ever seen a car like this or owned a six cylinder A-Body with this option? Any and all info appreciated. Thanks!