Certain non sequetional fuel injection systems could run without a tdc sensor, thats why I want to see what you want to fit?
If you wonder why you can't calculate where the engines cycle is think of it this way, the distributor spins at half the rpm of the engine so the engine will make two complete revolutions for every one that the distributor does. The engine then reaches TDC twice for every rotation of the distributer, how can the distributer "know" which one of the times it reaches tdc it is about to be on an induction stroke or on an exhaust stroke? And if you have four cylinders how can it know which cylinder is at tdc? Have a look at the "chopper" under your rotor arm, if all the chops are the same then it has no form of TDC sensor, if one is a differant size then you could well have a crude form of tdc sensor right there.....
Very early injection systems dont care by the way, they just squirt all four injectors at the same time but you only have to move forward very slightly before the sytem will at least require a TDC sensor of some sort.....