You can't tell just by the lack of paint and calipers aren't really going to tell you enough as it's not just shell width but parallelism that counts. One way to check is to install the external bearing cups moderately tight and try to slide the crank spindle through them. If it lines up with both cups with no wiggling or forcing, you are good. If it requires twisting or force to get the spindle through the second cup, facing is needed.