Rob, Here are the 100D2 number locations:
1) Block: Starboard bellhousing flange. Below number six cylinder and above the stater motor. You will see a flat horizontal portion of the bellhousing flange on which is milled a smooth spot, facing upwards, on which the block serial number and engine type is stamped. Service replacement blocks often have not been stamped.
2) Cylinder head: Front, port corner beside number one cylinder. A square boss with a vertical face is stamped with serial number and engine type. This may no longer match the number at 1) above if head swops have taken place.
3) Inlet valve cover, front half: There is a brass plate carrying the makers name and stamped with serial number and engine type. It is about level with number two cylinder. This plate and the valve cover can easily be transferred between engines and is therefore not a reliable indication.
Hope this helps - the valve cover plate and the cylinder head boss are easily read, but the block is much harder being down under the exhaust manifold and often very dirty.
