318 build #2 "cost minded" for the '74 Duster

I think that manifold/header test is flawed. I base it on the fact that Holdener on YT tested a 300hp Crate Motor with the dual plane M1 intake against a JY 5.9 with a beer barrel intake and got virtually the same numbers. If dropping that extreme runner length intake won't pick up power, I don't think much will.

My opinion is that the real restriction on that motor is the cam, and until a better cam is swapped in the real advantage to the manifolds and/or headers isn't going to show itself. Not saying there weren't advantages shown, just that it was less than what it would have been if the exhaust had been the restriction.
when you add a 200 shot it will matter the question is how much prolly alot more then what they found na
hopefully soon i can say with my own build soon
my 318 from the early 80s picked up quite abit with headers as compared to manifolds and helped mpg
340 manifolds not so much on a mild engine
both those engines you quote have low compression as well
my 340 is a legit 9.99 comp ratio and a 8.3 dcr with a 218@50 454 lift 110 lsa ica 60 in at 106 it has a 68 340 drivers side and the jeep 2 1/8 pass side with a 3.91sg and a 650 dp it will smoke the tires all the way thru 2nd if i choose great street cam on 93 octane much more low end then the stock 340 cam