Flywheel Identification

A friend of mine has a flywheel he will give me if I can use it; however, he does not know what kind of motor it came from. How do I tell if it came from a 360? If I'm going to have my motor externally balanced, I assume I can only use a 360 flywheel. The only numbers on it are B228...not sure what this means exactly. It has metal drilled out in two different spots, so it looks like it is from an externally balanced motor but not sure.