Gordon:

I would just use the sub diameter tool. A star lap is used to adjust the action in a specific area, usually for parabolizing. your 2/3 diameter tool will do the same. Vary the off center distance and length of stroke to achieve the action you need determined by testing. Using a star lap on a sub diameter tool is a quick way to produce bad zones. It can be done but you will probably find my way best. I only made star laps on full sized tools. Usually I would just experiment with a pattern that seemed right for an over center stroke. Hope this helps, -Rick