True overlap likes long tube headers , but most wanting to run manifolds are probably not trying to push it over 350hp with fairly mild cams doubt even with something like an xe268h cam the difference between manifolds wouldn't grow much if at all, what I take away from it any 360 manifold is fine no need to spend $$$$ on 340 one's, and if you already got 318 manifolds on your not losing much, probably the same with 273 one's.
