So, maybe this is an ignition issue? slowly increase rpm, no knock, goose the throttle, and you get a knock? Is the advance working properly? You say you degreed the cam, but is the crank marker correct? Is the advance working smoothly when goosing the throttle? Is this a TB-IV ignition? Module could be doing funny things, or the pickup. Inspect the cap and rotor?
We test ran with 93 and 1/2 pint outboard oil and got the power back BUT developed a hi rpm under load knock from either 6 or 8 .Raise the idle slowly up to 5 k and you dont hear it, raise it quickly no load and it clanks.As little as 4 deg makes it disappear no load.customer said it happened powering up . Will have a update as soon as I get it to take apart AGAIN.