New 3" exhaust with 2.5" Tailpipes

While contemplating what exhaust to get for my 512 RB, I went back to the book that I used to guide my build. Andy Finkbeiner's "How to build Max-Performance Mopar Big-Blocks". In the exhaust section he reaffirms the work by Jim Hand and states that the 3 inch rules only goes back to the muffler. I have taken a snapshot of the section of the great book where he covers that. If I violated copyrights, Please delete and I will type it. The book is great and I hope that me posting it will help sales instead of taking sales away. If @AndyF has any further comments from when the book was written, I would love to hear them. this makes the Pypes offering very attractive for my street/strip 73 Scamp.
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He covers mufflers as well.