1965 Formula S 5800 miles

pbiggs said

I have not found any other applications for the #541 or #548 (reverse flow mufflers). It seems they were only for 273 HP's. Can't be 100% sure though.

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Just curious. I have heard them described as a "low restriction Hemi style muffler." It would be easy to use a muffler from another year/model instead of building something specific. Thanks for the info.