Have you seen this?
Header Design Calculator | HorsepowerCalculators.net
I remember back in the mid 50's when Chrysler really went into sonic tuning. There is one version that has a four bbl carb sitting over the coil spring and feed the opposite side of the engine. Really long intake length yields low RPM boost. Mid to late '50s, Hot Rod magazine ran a tech article. It had the formula for calculating header length for any RPM range you desired.