You can check for the need to face a BB shell. First remove all paint from the faces. Screw the cups in until they just contact a .010 inch feeler gage, then use .008 and .012 feelers to look for high or low spots around the face. If those limits are exceeded, you need some facing done. The idea is to make the faces square with the threads, in addition to being parallel to one another.

When I switched several bikes over to Campy ultra-torque cranks, I found none in need of facing and all of the BB shell widths were very close to the nominal 68mm. With the ultra-torque system, the BB shell width must not vary more than plus or minus .8mm.