Warren,
There was a recent thread here about our beloved SHP engines,
the vast manufacturing tolerances employed back in the day,
and how these tolerances effected the compression ratio,
and ultimately the power output of that particular engine.
Indeed, one member here posted that an L/72 ( 11:1 compression )
actually spec'd in under 10:1 compression. Another member
wrote about deck heights being different by as much as 0.020
So, you can possibly see why your particular BB ran less than steller.
Needless to say, I will never build another engine without blueprinting it first.