The early belleville spring will handle more line pressure before it flips over/inverts. If you look closely at your belleville spring, it has wear marks in the middle where it should never contact anything, meaning it was flattening/flipping over from line pressure and middle was contacting the ring gear. With the later belleville spring, and if that clutch pack is shimmed toward the loose end of the spec, the oem spring will go flat/flip/contact the ring gear with as little as 130 psi. When that clutch burned up, it gained a bunch of clearance so even if it was shimmed properly, it could have still flipped and rubbed and unloaded the clutch/allowed the piston to over extend and pop the seals.
I love seeing guys tear into their own tranny, it's the best way to learn, and the only way to efficiently hotrod these trucks long term because they all break eventually, it's all about how much it costs to fix or how quickly you can make repairs that determines if you'll make the next race event or weekend burnout contest!