Pinging B$@&%@rd 440!

MP 284/484 cam installed at 104 (4 degrees advanced)

Was the cam degreed in?

Have you done a cranking pressure test?

Have you tried adding some 100+ octane gas to the tank to see if it cures the problem?

Have you tried reducing the timing a degree at a time to see how far you’d have to go to get it ping free?