Small Single Exhaust!

The mate to the Big Single Exhaust thread...

So I'm doing my half-*** resto on a 69 Barracuda with original, unmolested 318, stock heads and 2bbl carb. I'm liking the 2 into 1 "Y" pipe from Accurate and I want a standard, "quiet" muffler essentially following the factory setup.

The complete kit from Accurate uses a 1 7/8" pipe after the Y but they offer the option of a 2 1/4" outlet.

Would there be any benefit/advantage to the larger diameter or any potential drawbacks to using it?

My first thought is that even a standard muffler will flow better at 2 1/4" than a smaller diameter.