There are 2 TDC's for each single rotation of the distributor -- the crank turns twice for each crank rotation. You have to be on the correct TDC -- you must be at TDC at the end of the compression stroke. I usually stop short of TDC -- have the pointer pointing at where you want the timing to end up - 12, 14, 16 BTDC on the compression stroke. Stab it there with the module plug about halfway between the t'stat housing and the a/c bracket - that'll give you the most room for adjustment. Have your timing light handy. Fire it, remove the spout, and set the timing where you want it - plug the stout back in. Let it warm up before timing it.
If the car runs halfway decent and is in time with your timing light (and the TFI isnt smacking anything, like Michael mentioned), it should be 'in time'. If this is the case, it is not 'one toof off' as people like to say. The only way it is 'on toof off' is if you have an interferance issue, which is why Michael was conveying.
Good luck.
Good luck.