Even without looking and listening, I'll put money on it. One reason is the narrow, specific rpm range of the knock points to this as the problem because the harmonics--sping float/whatever vernacular--in the pump spring would come into play at a specific rpm.

The main reason is that incorrectly installed eccentrics seem to be a common problem, even with "professionals" (professional means that a person makes money at it, not any level of skill or compenticy.)

Out of the at least dozen times of being into the chain/gear, I have almost installed it incorrectly a few times. Strong mechanical aptitude and attention to detail will catch the problem before torquing the cam bolt, as I have caught myself getting ready to do the dumb stuff. (Yeah, I'm guilty of the dumb stuff too. As an old teenager, I had a mopar eccentric fall off a couple of hundered miles after the repair. Loose bolt, installed incorrectly--whatever. After it falls apart, does it really matter why?)

The eccentric has a tang that rests in a recess of the cam gear. If you study it and dry set it, the eccentric will fall into place and hold tightly with just a tad of hand pressure without bolting it on. It will have a caddywampus look in relation to the cam gear.

Do not start the engine again. If the eccentric falls off, there is a good chance that it will drop into the chain and the bolt will fall into the oil pan. All this can net total engine destruction. If someone can get pictues of the cam gear and eccentric, I'll try to point out the way it installs. Of course this involves pulling the cover.

Again, I'll bet money on this one. Any takers?

By the way, I haven't seen everything, but I have never seen a pontiac head/valve that doesn't have double springs.