Suggestions for muscle car sound muffler without drone

Your thread and your travels are very interesting. Up until now I have never seen anything regarding these pipes. I don't get much from youtube videos because it's coming from little speakers and the person recording always quickly revs the engine up and down. That IS NOT the problem. The problem is a constant RPM while you drive where that resonance gathers and grows and makes you feel numb. Now for a few questions.

I assume the length of the 90 was also calculated into the overall length of the pipe?

The graphs you're showing, is that from the phone app and the screen on your phone? I see one shows Samsung in the corner so I guess it is.

Looking at the plot, I see the spike and from reading your post, I gather that that is the peak resonance. So when tuning the pipe, that's where you came up with 125hz as the target to tune to. Am I following this correctly so far?

You went with a smaller diameter pipe and it worked. Based on that it's the length that's important because the length is what controls the return time of the sound waves within the exhaust system, did your research show at what point the smaller diameter of the resonator pipe might negate it's ability to perform it's function?
How did you determine that a smaller pipe would still work?
Does a smaller diameter pipe factor into the length equation? I would assume not because we're dealing with the distance the waves travel and not the volume. But would too small a resonator pipe not have the desired effect on the larger mass of exhaust flowing by it? I'm wondering if a 1.5" pipe would work still on a 2.5" exhaust system? The smaller diameter pipe is certainly desirable as far as fit and discretion.

Thanks for sharing.