What's wrong with my motor?

340sFastback said
Maybe pistons are not installed correctly and the valves are hitting the pistons because the valve reliefs are not oriented correctly?

Short block has been together for about 17 years and has always run fine. Piston's didn't come out, and these are the same heads I had on the motor when I owned it the first time.

Used to have a stethoscope, need to track it down or get a new one.