Hmmm-
I just compression checked the used 350 in my son's 62 pickup at 162lbs average per cylinder ... when divided by 14.7 comes up to 11.02/1 YEAH!! We live at about 500 feet above sea level.
As Techinspector said, using this method would be dependent on knowing where in the stroke the intake closes. You'd lose some compression if the piston is already on it's way up when intake closes. Not sure your method could ever be mechanically accurate and I think your 14.7 figure might be a little generous, but this is an intriguing method of assessing used engines.