Might need to get them checked with a road force tire balancer. I had tires on my Honda pilot that balanced fine on a regular machine but still vibrated. Had them checked on a road force machine and they found a blown belt. My tires were new also.
Overloader springs give it a permanent stiffer ride which isn't ideal when unloaded. You have the option with airbags to run them aired down to keep the factory ride.
You could try letting out the limiter strap and put some tension on the front shock spring of the skid. Basicly transfer some ski pressure to the rear.
Have you tried another coil? The stator could still be an issue there is a lighting coil for the lights that is separate from the pulse coil for ignition.
This would explain the running really well part before it quit. When a carbed machine seems to be running better than normal there is a good chance it is running lean.
That is the way that style off clips looks. There would be some major scoring in the cylinders to have any parts of those clips get above the rings. I think the debris is from the piston chipping. Looks like it may have been too lean or too hot or both. What color were the spark plug tips?