The trailing edge of the rotor tip needs to point exactly at the number one contact in the distributor cap with NO clockwise backlash, when the cam screw is tightened. It may take several tries to get it right because when the cam screw is tightened it has a tendency to move the points cam in the clockwise direction, adding backlash in the wrong direction. There will be backlash, (rotational movement at the distributor shaft) as long as all of the backlash is in the counter clockwise direction after the cam screw is tightened, you will be close. Points gap effects timing, more gap advances, less gap retards . A points gap, anywhere from .018 to .022 will run pretty good. For exact timing, the points should be just ready to open when the timing pin drops in place with the spark lever fully retarded. Most seem to use a happy medium gap of .020 . I like mine slightly advanced and set the points gap at .022 . This is as as advanced as you can go without starter kickback. Retarded timing causes the manifolds to run way hot and throttle response to be labored . Performance will be very weak, it also causes overheating. When setting points and timing, it is always best to remove all of the spark plugs. Fighting compression makes timing difficult. When it nears the timing mark, compression increases causing you to go past the timing mark or high cam on the points cam.