Ignition timing is not adjustable on your engine. Older engines have a pick up coil, or points, inside the distributor. Rotating the distributor changes the position of the pick up coil or points, which is what causes ignition timing to change. On your 2001 4.3L, the crankshaft position sensor takes the place of a pick up coil or points. The sensor is mounted to the timing cover and does not move. Moving the sensor changes ignition timing, but there is no way of knowing where. This is why the crankshaft position sensor relearn needs to be done if the sensor or the timing cover is moved, removed, replaced, or disturbed in any way, (base timing will not be correct). Rotating the distributor on your engine does two things: one, it aligns the camshaft position sensor with the camshaft, and two, it aligns the distributor cap so when the ignition coil fires, the air gap to the rotor is at a minimum. Rotating the distributor has absolutely no affect on ignition timing. The adjustment is called "camshaft retard" or "CMP retard". If CMP retard is set correctly, you can disconnect the camshaft position sensor and the engine will start and run just fine. Cylinder misfire detection and cylinder identification would not be correct, and the SES light would come on, but you won't notice any difference in the way it runs.