Chasing a clutch or an injector ?

[Hammerhead]

You're far too vague on details to support or discredit any injector issues.

The bits of pedal reaction issues you describe, sound distinctly like a broken spring in the clutch to me. Paint on the clutch springs is meaningless, I've seen plenty of broken springs with paint still on them.
Try greasing the release bearing, they usually get neglected and it may just have dried crud instead of good grease in it?
Clutch choices are the atypical Eaton EasyPedal, which can handle the torque output of a 560hp just fine.
A Heavy Duty option is a Lipe 1, but it will take some getting used to as it is a direct clutch as opposed to the Eaton. They are a little harder "push & hold" than an Eaton, and they engage more aggressively. If you don't like always starting in low gear and finessing the clutch pedal, it's not a good choice.
*note* in my opinion heavy starts at over 150,000lbs, so the Lipe is rarely my advised option, but you asked.