Hello:
Intrestering post, lots of good information. However unless I missed it the horsepower ratings used are factory published figures. One item that some of you may not be aware of is that at that point in time the Insurance companies and the auto industry were in a tug of war of over horsepower. It is entirely feasible that the 67 383 A Body was factory detuned on paper too satisfy insurance companys.
Now mind you I do not doubt the equiptment was a factor, it certainly was. The exhaust manifold on driver side was a comprise at best. Unfortunley my stock camshaft is long gone so I can't help there. I can tell you that a bigger cam with an Edelbrock DP4B and good carb feel much better in seat of pants.
Any way my opinion on this is to not rule out the factory playing numbers games. My 67 GTS was insured as a compact car.

Maynard