a little thing to put in your pipe and smoke: demands on these manifolds were marginal

The typical engine around here would not be hard pressed to breath heavier on those manifolds. The displacement 428+ 0.030"x3.98", rather mild flat tappet Hyd Cam and RPM were no where near the hunger of many of the solid/hyd roller, Big Stroke & Bore wild Alum. headed and solid/hyd. roller cammed monsters that are run on this forum with many of those same tested manifolds. \\\

At least the open headers were not a restrictive street/strip tailpipe and muffler system that said others may use..