I recently pulled the headliner out of my 71 demon which should be the same as your duster. It has the 6 bow style and had most of the bows mounted into the lowest hole of the 3 options. I took pictures of everything, can email them to you if interested.
Agreed, rallye dash frames are out there but at the time I couldn’t find any locally and crazy shipping costs were deal breakers for ones that were out of state.
I also figured this way I don’t have to mess with the vin tag!
I just modified my 71 demon dash frame to accept a rallye gauge set. Used an extra 67 barracuda dash frame I had laying around to make cardboard templates. Only took a few hours but mine was completely removed from the car and already dissembled.
it’s pretty easy to apply voltage to the new gauge after the face swap to see where the needle points to have a reference. At 12 volts it’s roughly in the center on the gauge.
Part number for the tach is 82181.
Dash isn’t installed yet, just finished modifying the frame to fit the rallye cluster and am now waiting for my reproduction bezel, has been on back order for months. I also converted my amp gauge to a volt meter using info from this site.
I just mounted this Stewart Warner tach into the rallye cluster for my 71 demon. Looks fairly close to the factory unit. Still need to paint the needle orange.
I believe the deluxe interior option had the chrome arm rest bases along with wood trim on the dash and door panels, carpeted side panels in the fastback area, seat medallions and pedal trim.
I have owned 2 68’s with this package a 318 car and a 340 formula S.