340 Manifold numbers question

So I was surfing around and found this excerpt from an article....very interesting...

Excerpt from the Mopar Muscle test on a 300 HP crate 360

Log 318 manifolds

For our baseline test, we fitted the 360 with the lowest of exhaust low, a set of stock small-passage 318 iron exhaust manifolds. Bolted to the manifolds was a set of 21/4-inch head pipe extensions 24 inches long. So equipped, the 360 put out a respectable 311 hp at 4,600 rpm and 403 lb-ft of torque


Log 360 manifolds

We moved up a notch from the early 318 iron manifolds to late 360 iron log-style manifolds. The 360 manifolds are nothing to look at, but the internal passages and outlet are significantly larger than those of the 318 pieces. Power was up a little, moving to 314 hp and 407.1 lb-ft of torque.

340 Hi-Po manifolds

Our final test of factory iron was a set of rare and expensive early 340 high-performance manifolds. With the 340 exhaust, the 360 inched up to 315 hp and 409.1 lb-ft of torque, which represented very little gain on this engine.

Really not a lot of gain using the 340 manifolds for the cost involved.....if true.