Originally Posted by polyspheric
The cross-ram (413 Chrysler F, G 413 RB; 383 B, MW) was specifically designed with runner length to add torque based on the engine's power rage (2,800 and 5,500?). Small plenums, small carburetors, and high velocity in the runners. Since the left and right manifolds are separate castings, an original manifold ($$$!) will bolt to any B/RB engine, shorten and re-attach the runners to your calculations.
I spent many happy hours in an air-conditioned 300F convertible back in the day, and its "manners" never betrayed the plumbing under the hood.
Too long for big cams an good heads.

What would a manifold be with runner length tuned for 7,000?
Tunnel ram - the runners just extend vertically.

The Weiand 6-Pack offers some ideas, see my comments here: http://victorylibrary.com/mopar/weiand.htm

You forgot to mention that Chrysler made three different intake runner lengths from 1959 to 1964 in the 300 Letter cars, long length with the divider from the carb plenum to the heads, medium length runners with a small amount of the divider wall removed near the heads and the shortest ones that had no wall between the runners up to around the middle of the manifolds from the heads: scope:
I think the last ones where the shortest ones and probably made the best combination of power from the idle and low RPM (under 2500 RPM) light part throttle operations up to wide open throttle work twocents

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)