Okay. Ive done the manifold thing quite a bit. I have not tried the cherry bomb/resonator after the axle so I cannot speak to it other than anyone I know that has tried it says it works.

Here is what has worked for me: a factory type full length replacement muffler. That's it

I have used the Dyno Max Super Turbo in both the 747's and 748's sizes. Initially, there was almost no drone, but soon after the drone starts and builds as they age.

Also, your gear and car weight will either make it better or worse, relatively speaking. More gear and less weight, less drone. Similar system on my light weight 383/4 spd/3.91 gear car had considerably less drone than on my heavy weight /3.23 gear auto car.

Good luck