[NeighborsComplaint]

If you can rule out rocker/retainer interference, that is one variable out.

As others have said, that backwards rotation after cutting the ignition would normally indicate excessive cranking compression or too much initial advance. How did the engine crank on hot restart? If it "groaned" slowly before spinning, initial timing is too far advanced.

Retainer to rocker clearance needs to be ruled out as a cause. You should have daylight between the rocker bottom rail and retainer. Short Dport pushrods with a 1.7-1.8" installed height can be the cause. This will cause an intake valve to hold open and cause an intake backfire also. Longer pushrods and/or offset locks/keepers can correct this.