[Barnsnake]

Hey Paul,
I'm no EFI expert so I'll stick to the basics. Given the things you've tried, it appears you're convinced it's pre-ignition/detonation knock.
When this engine was rebuilt were stock parts used? No high compression pistons, etc?
Were the heads milled and/or the block decked? Was the cam changed? Do you have the equipment on hand to check whether the cam is in time?