Okay Tim, you've been very helpful
I came up with
CON4 E207
So, it must be a 57' meaning it has hydro lifters. That would make sense. I found some instructions for making those adjustments.
Originally, I set out to check the lash as a beginning to diagnosing a valavetrain type noise I'm getting at speed under partial load.
It always occurs in high gear aprx 40-50 mph. Not on decel, not under heavy load, not during no load reving. Maybe it's a defective lifter. But from my experience they bleed down and tap consistently.
I would normally lean towards a worn bearing considering the symptoms but the sound is high pitch similar to a failing valavetrain component.
