Conrad. If you get a S14 block and put it beside an M10 block you will easily see the difference. The S14 block has an oilway down the side, so when you fit the M3 head to your M10 block, it produces a very big oil leak, and the engine soon produces strange knocking noises. LOL... I know, when my S14 block cracked, I've tried the M10 route. (unsuccessfully!!!)