As long as the rotor points to number 1 plug wire on the cap and you have it properly wired, it can literally point anywhere as long as the wire length will allow it. Most often, adjacent items, i.e. firewall, coil, manifold, throttle actuating device or other items dictate the final position dependent upon distributor type.

 

Depends if number one plug wire is at 4 o'clock. Find number one wire at the cap. Put a chalk mark on the distributor at that point. Pull the cap. Bring the motor up to tdc. The rotor should be pointing at your chalk mark. If it is, then you are good. The relative placement of the rotor is not in itself important. I think that's what you are after.

 

It can be anyplace, but originally, number 1 is just to the passenger side of the center of the distributor. View A...... http://www.trifive.com/garage/55%20Chevy%20Assembly%20Manual/221-11.gif ..... This allows for correct timing without the vacumn advance hitting anything.