i'm not sure if i'm following your question correctly (you are using a standard crank trigger correct?) but you do not want to phase the distributor at TDC because when you back the trigger up to where you want it to fire the rotor will not be in the proper position. you should always accurately locate TDC and have a firm reference point for it. once you have TDC located back the engine up to the rough point you want it to fire (30° should be a good starting point) set the trigger at the magnet on the trigger wheel and phase the rotor to the number one cylinder. this should give you a good starting point where you can fire the engine and see where you're at for final adjustment. once timing is set final distributor phasing can be done with a cap with a hole in it (#1 cylinder) and a timing light if you want to get critical. personally i will absolutely not use any timing light that has adjustment on it always use a standard plain jane timing light and go by the degreed damper.