Thanks Doug.

With an Estes E9 dummy engine installed, the center of gravity (CG) locates just past the mid point of the launch lug, which I attached as per your design. The center of pressure (CP) should then be 2.60 inches aft to achieve one caliber of stability. I'm going to proceed with Kevin's suggestion just to be on the safe side and will post my findings here. If I can devise a way to attach a string without damaging the finished rocket I'll also do a swing test.