Got a 210mm, two pin flywheel from a gas engine here at the computer with me. Laying it over a turbo diesel flywheel that is handy there is the dimple like CRSMP5 said, right next to the bolt hole, that lines up with the TDC mark on the 200mm TD flywheel, and a second machined notch a few degrees counterclockwise for the gas TDC.
The part number for the 210mm is 027 105 273; hope that helps