I myself would skip the Magnum manifolds since there gain is not big over the stock parts. A noticeable gain is not what they would provide unless you thought out the build completely. Headers would be the way to go.
From a member here, who followed his suggestion and purchased Hedman headers because they fit. Thanks have a set of next name headers, a Summit knock off or reselling another brand, IDK, but it required the previous owner cutting the frame rail to install. Pictures below where you can see the drivers side frame cut and grinder on. Big time. Spend for the Hedman’s. See how much clearance they have over where the frame rail was backed up? It’s huge!
Off of the header I ran 2-1/2 exhaust pipe I cut & welded myself. Depending on exactly how your truck is set up, it can be easy to a bit of a PIA, but easy enough a novice can do it.
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