69 cuda with 360 stroked to 410 Way the hell to loud.

Cross overs (H, or X, your choice) and the largest/longest Mufflers you can fit and afford. Go as large as possible on the pipe diameter as you can fit or afford too.
Auto Exhaust Science

Power impact can be minimized, but most folks go too small or try to pinch pennies a bit too much and then lose big power. Quieting something doesn't need to rob power, it can still flow (and flow it must), the idea is to reflect some of the energy and reduce the sound pressure which is why larger diameter pipes can help - deepens the tone and kills some of the rasp, pop, and harshness.

Dynomax makes some great stuff and others have recommended same or similar above.