Pull #1 spark plug, put #1 cylinder at TDC on the compression stroke. Verify that you are on the compression stroke by holding your finger over the plug whole, you will feel the air coming out from compression. Just bump the engine over a little bit at a time, don't spin it. Mark the distributor where #1 plug wire is. Once you are sure you are on the compression stroke, drop the distributor in with the rotor pointing to the #1 tower on the cap.