Suggestions for muscle car sound muffler without drone

The 90 I used had a flare you can see in the photo and it was long enough to allow some adjustment. You could also make a cap for the end the you clamp on to get some length adjustment. If you did both you would have inches of length adjustment to the length if you had to tune it. I don't think you'll need to tune it if you measure the actual frequency of the drone and make it for that frequency. If the drone is really bad use the same size pipe for the resonator as the main pipe. I got away with a smaller diameter pipe but I also had mufflers that reduced the drone by 12db. Dynomax VT mufflers are advertised to get rid of drone but they just reduce mine by the 12db.