The C spring replacement was copied from one on a CC Johnson Ballard. It is basically a coil spring with a plunger. The plunger is also an over travel stop for the trigger. The tension from the coil spring on the trigger adjusts the sear/cock notch engagement.
I have another custom .22 Ballard with a similar C spring replacement. It is speed-locked and has a custom trigger with a built-in shoe. Unfortunately there are no markings on the gun to indicate who did the work on it. This one also has spring installed in the breechblock that holds the lever at 90 degrees when the breechblock is lowered. I assume it was done to aid in re-loading. This Ballard will be going to Mike at Crossno Gun Service soon to have the Pope-style hammer conversion done.