Early A Body HP 273 exhaust
273 1964-66 stock exhaust was 1 7/8".
On my Valiant, the local Midas made me a nice system, :thumblef:
about 10 inches from the manifold its up to 2 1/4".
I am using Dynomax Super Turbo mufflers,
a good installer can make a great system,
and save a lot of hassles.
I rebuilt a warmed up 318, to replace my tired 273.
If you look close you can see the chrome tips in the second picture.