This goes way back, so correct me if I'm wrong. Above the water pump, just below the intake on right side, there is a notch between a strut and a raised boss on the block. The width of this notch is different on 283 and 327. Used to use this when street racing to tell what engine you were actually up against. I can't remember how the width varies for which engine, but it is noticeable, say 1/4 inch wider. If someone with both engines laying around might check on this and clarify. Been too long, might have been on 265 to 283, but I'm thinking it (the difference) was on the 327.