If something appears too good to be true. Don't trust it! I would take the block somewhere else and have it checked. Exact same thing happened to me. Had a block sonic checked and numbers were really good. Had it bored to 4.400 assembled the motor. But didn't install, I came across a good deal on a KB solid low deck. So I sold the short block to a guy in Cal.. Months later I got a call from the guy . He had the motor dynoed and it blew up on the dyno. The cylinder walls were paper thin. Lesson to be learned, if you have a block sonic checked. Make sure the equipment they are using is of top quality, not chinese junk. If it checks out too good to be true. Don't use it.