I understand your point that 318's can be made to produce, but one thing I am trying to explain is that the later engines were rated at net horespower which meant that they were rated with the accessories attached and in some cases through a transmission while the earlier engines were rated gross at the crank without the accessories attached. So my point is that an earlier build engine was not necessarily less power than a later built engine.
The exception to this is the 1972 and up engines that were detuned primaily through lowering the compression. This is why the 400 and 360 initially got such a bad rap as a dogs. With decent pistons as proven over the years these engines can be real power houses and essentially that is primarily the main difference between them and thereelder resped cousins the 340 and 383.