Going 2-1/2” up to and including new 2-1/2” mufflers will make a noticeable difference. At your power level the 2-1/4” tailpipes will not be any real restriction.
The exhaust gasses have cooled and condensed at that point so you’re good with the smaller pipes after the mufflers. The car will be a little quieter with the smaller tailpipes too.
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1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
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