What does the Lycoming Maintenance Manual / overhaul manual say about power off sudden stoppages?? Does it even define this situation as a sudden stoppage?
Speaking as an A&P, that would be the first place I'd be looking. My initial gut reaction though... tear it down.
I don't think the Lycoming manual addresses this specific issue, but there is a service bulletin out there that states that ANY prop strike of ANY surface or object requires a teardown. Prop touches a blade of grass while landing on a grass runway? How far does one go to oblige that SB???