5.9L Magnum questions

On a mild 5.9l I wouldn’t overly worry about the manifolds, headers definitely better, not huge hp difference between manifolds.
Gotta say I disagree. If you leave the stock cam in it I’d agree with you, but any increase in performance be it from a cam or compression or other is negated by putting manifolds on it. Especially so with the worst small block manifolds there are, the 273s.