In the muffler business, they call them Cadillac mufflers. Full flow, but whisper quiet while puttering about. You do hear what's going on when you step into it though.
I have them on my '49 3100 with a 350 with just a bit of a cam in it. The muffler shop should know what you are looking for if you tell them "Cadillac mufflers".

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission