Maybe the Harmonic balancer did slip as they are a 2 piece design GM stock or what merc uses. They have an inner and outer. Also bad virbration can mean a down cylinder or 2 or more especially on the same bank. We had a 496 that 4 and 6 were down and that thing shook so bad - thought the boat was going to come apart.

OSP. Harmonic ballancer can slip on the rubber dampener. I have heard of them actually coming off on the dyno before...going to have to look it up on you tube now!

The oil filter will tell all

Yup. More ProComp schit. So much for SFI on their stuff. They probably Frauded that on there too.