383 knock goes away on warmup

Hey All
I have a knock that is only heard on start-up when cooled off or not run for a few hours. it goes away at higher RPM or as soon as the engine is warmed up.

Oil pressure is good (near 80 lbs at idle and over 40 when driving).
I checked the plugs and they are black with soot and wet signaling rich mixture and possibly too cold a plug.
I have added octane boost and it helps but not 100%.

Here's where i am right now;

I ordered a set of plugs one heat range hotter
I added a can of Seafoam treatment to my fuel to clean system
I backed off the timing and it helped a bit.
I am trying to nail down the CR but i didn't build the engine. I have bore, stroke, gasket compressed thickness, head volume, flat-top pistons, so best guess it is not over 10:1.

I don't believe it is a rod bearing. I think it may be excessive carbon build up in the combustion chambers so we'll see if the fuel additives help.

It may be piston slap. I have been told it could be stuck lifters but sounds low in the engine bay. I will check proper rocker gaps when replacing the plugs.

I will post results when I have run the chemicals thru and installed the new plugs. Perhaps jet size changes to lean mixture?

Any other suggestions?