Davis You are correct if you paid him to build the motor there should not be any reason for you to have to check any bolt after recieving the motor unless stated by the builder when you picked it up. If he installed the adapter then he is responcible for it being loose due to the wrong bolts .
Which in turn lit the fuse on your time bomb.
Apparently after installing the washers you didn't see a loss of pressure so you must have figured no harm no foul and made the passes that night. But you did lose a large amount of oil so the bottom end if anyway possible should have been checked, but since your builder didn't tell you that you felt it was ok.
9 passes is not much runtime and you relying only on his word, you didn't know better and ran it.
People do make mistakes, everyone does. But how they handle themselves after is what makes them an honest person.
Gotta go for now but I can ad more later if ya like .
Donn