My money is on multiple keyway on the crank sprocket. But, try this.
Pop the valvecovers...cycle the motor until #1 comes up on TDC compression stroke. Now keep cycling the crank another 360 degrees, and watch the rockers for that cylinder. "Dot to Dot" is TDC/Split overlap. In other words, when the piston is at TDC of the exhaust stroke, the exhaust valve is just touching down on its seat, and at the same time the intake is just rising off it's seat. If your cam timing is dead on, both the intake and exhaust valves will be open the exact same amount.