A couple of things presented themselves after maikng my two halves whole.
One is the natural tendency of something pliable to resist maintaining it's shape when holes are cut into either end, like the ball does have. The other was how to mount my two pieces onto the engine pylon while still allowing easy disassembly?
One answer, was to fabricate a "collar" that fit into the sphere halves and then the pylon mount. Did so with alumium and styrene (again!) and now it not only holds it's shape but will go in, or come apart as needed.