Well with all the problems with phasing distributors, I thought I would take some pictures on how to make a tool and phase your rotor in your distributor. You will need an old distributor cap and a timing light.
The first step is to modify the distributor cap. The V shaped notch on the top is to check and make sure that the top of the rotor is contacting the terminal inside the cap.
I cut two large windows so I could better see what is going on.
Next I marked the rotor with a Sharpie.
Putting everything back together
In this picture I hooked up the timing light to the post I wanted to illuminate. This picture was taken with the engine running and with the timing light hooked up. Note that the mark is lined up with the post. This is what you want.
Hope this helps.