Big Block Exhaust Manifold Comparison?

I think Rusty is correct...there won't be any difference. Those ratings were all over the place depending on marketing, sales and model selection. The 383's HP really meant the build had a 4bbl, windage tray or other such accessories. They published all manner marketing ploys like 383's got 440 heads. Some A bodies had 383's stamped HP and some did not.