I've put a Mopar Performance dizzy in my 440 (.40 over, Eddy heads, around 9.2:1 compression, 60303 cam, 16* initial, 34* all in). I am getting a part throttle rattle at higher engine speeds (75mph with a 2.76:1 gear ... sorry, no tach). The engine builder seems to think it is detonation especially since it seems to get more sensitive as the engine warms up. It doesn't sound like any kind of ping or rattle I've hear heard. And it doesn't make the noise at or near full throttle.

I pulled the initial back from 18/36 this morning to the 16/34 I listed above. It still does it. And yes, I pulled the vacuum advance hose off and plugged it to make sure it wasn't the vacuum advance (I've also gone 2 turns CCW with the adjustment in the vacuum canister).

The engine builder gave me a bag full of springs to try out but they look to be for the older Mopar Performance Dizzy based upon what I can find here with the search function.

So, here's a picture of the springs that are in the dizzy now. What would you do?