distributor and advance

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1987 r20 pickup 454
All: in fighting my bogging problem, i replaced the pickup coil in the distributor, when I was removing it and before I loosened anything I marked three points on the unit and once i put it back in i lined all three points up, but when i started the truck up i had to rotate it almost a halve the distance to the next plug. and with the timing set i am not even close to my marks, actually quite a ways off. any ideas what would have caused it. In the original position my crankshaft mark is not even visible, it is about 12 o'clock instead of matching on the indicator to set my degrees.
thanks