Yeah, the 4.9L is a tough engine.
Your timing gears are the very first I have ever heard of stripping out like that
and I have owned several 300ci from the 70's.
Ten years & 65,000 miles ago when my 87 4.9L was rebuilt and balanced;
both timing gears were replaced with metal racing gears.
The engine has a whine when idling,
sounds like a Super Charger or transmission going bad, but its neither.
The metal gears are supposed to last longer than the composite gear.