[HeavyJ]

While running at idle, pull one sparkplug wire at a time and see if the knock goes away. this usually works on a bad wristpin at idle, but could tell if you have one at your rpm range or at least narrow it down to which cylinder is making the noise. Could possibly chock the wheels, set brake and put in gear, have someone power it up to the rpm range while you listen with a piece of hose or mechanics stethascope to pin it down.