yeah i heard the same thing about those manifolds, so i hear ya. i got the super 40's on mine, too quite! go with super 44's!
but ya know how the flow masters have the flat look, i just tilted them both on each of the driveline side of the muffler but idk where the original mufflers sat on these trucks. but if it's too quite youre too old!
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1970 C/20 4x4, 350, sm465, np205(She tipped over... total rebuild from the frame up!)
ya gotta keep on keepin' on,
Life's a garden, dig it!