360 LA turbo exhaust question

Metal balls would be melted bits of piston. My guess would be from detonation. Did you ever run it lean?

Breaking a ring land is possible, On oem pistons, if the gap was pushing .030” I would be doubtful. When the ring land let’s go, it takes the head and valves with it. Along with some bent pushrods. Turbo would be shelled out. Burning the piston from running a lean mixture melts the tops and plug and the aluminum oxides with the excess o2 and then changes phases from solid to liquid. Keeping it rich and free of o2 prevents the phase change because it is extremely hard to melt Al without oxygen present.

Next motor, after a few passes, try pulling every plug and cutting them open. AFR gauges are a great tool, but every cylinder and injector is a little different.