Bantam 1800 diesel TDC

First I need to know if it is the: DV4 TD (69 hp/51 kW) turbo-Diesel or the DV4 TED4 (90 hp/67 kW) turbo-Diesel 16-valve

TDC on that diesel is not in any way related to TDC on a gasoline engine. Top Dead Center, and the # of degrees before TDC is when the spark plug fires on the piston's way up on the compression stroke, on gasoline engines. Your question is "how do I determine TDC...." well that is when the piston is all the way up. But you don't set the timing like that on a diesel. It explodes the fuel when there is enough heat and compression, it does not have spark plugs that need to be timed in the conventional sense as gasoline. There are others on this forum that know far more about the Duratorq, but if you do get back and tell me which engine it is I can do a bit of research

The TDC on this vehicle is set using a special tool which fits into the side of the engine block. A plug in the side of the engine block is removed and a special tool 'Pin' is inserted. This is basically the same engine that went into the Escort 1800 TDCI with a mechanical diesel pump. From then on the pump is loosened and moved to the correct position using a dial gauge. Its best to let the Ford Dealer perform this as they have the special tools