Example: Set your timing normally, let's say at 38 deg. Bump it over and align the timing marks to 38 deg on #1 compression stroke. With a small staight edge and a pointed sharpy, make a vertical line on the side of the dist cap and base at the center of #1 post. Remove the cap and align the center of the rotor with the mark you made on the base. Try to be as accurate as possible. Obviously you'll need an adjustable rotor if not using a crank trigger. That's it. Hope this helps,
Johnny