Big Block muffler choice

Hey Fellas,
1967 Barracuda 383 4 speed. Dunno if it matters but its a flat tappet .250/[email protected] think. Anywho, this thing has somethin to say and I wanna quiet it down. its a 3" exhaust. The 14" summit mufflers (turbo?) aren't doing the job. My question to you is....

1. Whats the longest muffler you have run? 20"?

2. Did you choose a 'straight through' or chambered design.

3. I am looking at the dynomax 17233 ultra flo and the half the cost walkers quiet flow.

4. Does running a cat help the situation?

I dont want to kill the power, but rattling the neighbors windows every time I go out isnt cool by me.