SB vs. BB

I had a co-worker come up to me this morning and ask "What makes a SB a SB and a BB a BB?". I told him its the physical size of the block itself. He then asked "What is the measurement that defines whether a motor is a SB or a BB then?" I couldn't answer him.

Does anyone know exactly or even roughly what the physical defining dimensions are that classify a motor as a SB or BB? If someone has a SB and a BB Mopar sitting in their shop, can you take a measurement of the block (height, width, length) and post them up with the CI of the motor. If it is bored and/or stroked, please post up original CI.
Author: 78D200