What kind of power are you talking? If you are talking a stockish 1977 440 and you want quiet, you don't need 2.5" dual exhaust. The best driving, snappiest throttle, best pulling 440 I ever had was a factory original 350 hp 440 in a 67 Chrysler. It had a 2.5" single exhaust.

If you are like most, and simply must have an exhaust system that is 50% bigger than you need, get a dual system with 2.5" headpipes, necked down to 2.25" mufflers and 2.25" tail pipes. Get the longest full body muffler that will fit from Midas. This is basically what the factory used on the highest hp 440 it offered. This will support an honest 375 hp.

I've made over 400 hp with that system with a DynoMax full body (25.5" long) 2.25" Super Turbo muffler (17747).

In the future you can step up the muffler and tail pipe size to 2.5" and easily support +450 hp.