Ok. Vacuum reading is steady but low.
I was leaning towards you having defective heads from the re builder like a sticking valve guide, not fully seating valve or a bad cam, etc. Anything going on with the valves or valve guides would've came out on the vacuum reading and compression test. And you had a steady reading which is good.
Your thermo readings on the exhaust ports were nice and almost even on all 6 cylinders. Indicating a steady flame on all 6 cylinders.
Your compression test was good, somewhat even. No excessive high or low cylinders.
Great vacuum reading would be in the 18-20 range. Your is a steady low 14-13.
So if you go back to the chart on the vacuum gauge pages, it's has defective ignition components as a probable cause.
That chipped tooth could affect the signals going to the ignition coils cause of that low vacuum reading.
I really feel you are close into solving this.
Crank bolt 11/95-9/98: 90105-16031
9/98-...: 90119-16006
Sprocket: 13521-62031