Load will be transferred through an eye nut connected to the piston and inside of the cup. This presents a space problem, as the threading on the end of the piston rod has to accommodate the diaphragm, the eye nut, and some sort of retention mechanism (like a cotter pin). Some preliminary options are:
Decrease thickness of diaphragm
As a preliminary guess, the diaphragm total thickness can be decreased from 0.625 to 0.375: