I had Full length TTI headers with Dynomax Ultra Flows and full length 2-1/2" tail pipes on my 440 Cuda, and I did not have any drone at all. maybe tail pipes will help.
Our exhaust systems are fairly different as I have shorty (unequal length) headers, a shorter wheelbase car, and different length exhaust tubing with a different engine. I don't think it can be fairly comparable car-to-car.
The Dart has a longer wheelbase than any Cuda. Yours is 111" and the 67-69 Barracuda/Cuda is 108". The E body Barracuda/Cuda is also 108".
