This is an interesting thread with a lot of good thoughts. I am hoping for a positive outcome soon. I'm thinking the single rudder pedal spring fix may be it. At least those are easy to get at and replace...
Have you tried giving the right rudder a good hard stab?
My C180 sometimes has the ball slightly off to the left after takeoff,
but a hard stab of left rudder puts the ball back in the center.
I'm guessing the tailwheel is holding a slight right set after applying a lot of right rudder during takeoff,
but that hard stab of left rudder puts it back in the center.