Back pressure doesn't make rod bolts come loose or aid in spinning a bearing.
I'll add this:
If the FAE caused enough back pressure to harm the motor it would be very noticeable right when it was first installed. Think about all those early styled catalytic converters. When they got clogged to the point of making back pressure cars would run terrible. It would be to the point they wouldn't get over 40 mph or so.
The FAE had nothing to do with the demise of your motor and I'm kind why anyone at Rambo would suggest that.
Gone, out doing soft recreational past time with overpowered boat!