I bought a nice quality old road frame from approximately 1980, so it likely originally had an old-style non-cartridge BB with a quality installation. I am installing an external-bearing BB/crank (SRAM S300/GXP BB, to be specific), and would like to verify whether the BB has been faced or not.

According to the Park Tool website, during the process of facing, "When cut metal appears in a complete circle, facing is finished." I do see bare metal all around the circumference of the BB shell presently-- does that mean the shell is already faced? Should I verify by measuring distance between the sides of the shell with a calipers in different spots?