I would not put one of those other big springs inside the original one. That can create a bind when it’s applied, then not want to fully release, and smoke the band. I don’t run the red sonnax servo but I know it’s not designed to function that way with the two big springs. And if I’m wrong, and it is designed to function that way, it’s news to me. The dual spring servo has a 3/8” rod, with a small inner spring, and large outer spring. I would get a new servo from A&A if it were mine to help the 2-3 overlap. Or just run it the way you have it and call it day lol. The 2-3 overlap will always be there, but minimizing it is the goal.