Install a timing tape on your balancer. It's very important to know what you are dealing with as far as timing. All 3 stages of timing, Initial,centrifugal and vacuum. The only other thing I can think of that can cause a knock that has not been mentioned is a stuck closed heat riser valve. This causes the intake manifold to become very hot, super heating the intake charge.
As a follow up to Steve's good suggestions,
Timing tape or use a set back timing light which can read the full amount of timing.
As far as the heat riser valves, I removed mine (from my Camaro and Chevelle) and installed spacers in their place which are readily available from the aftermarket.
Back in the day, the heat riser valves were problematic enough. Today, it is tough to find replacements that won't bind up after little use. By not having them, the preheat of the intake manifold is compromised, but it hasn't been a problem on either my 69 RS or my 66 Chevelle. Once the engine warms the heat rise valve should be open and is just a restriction in the exhaust pipes.
Just my two cents.