Nice find...
If it's not an all out motor, just dress the high spots & crack test it.
If that's all good, clean 'em up as they should be fine to go again.
(Looks like FOD from a screw thread or something)
How's the Ex quench pad on the head #1 ?
I can get you a single piston if need be + rings, clips & pins are also available as sets or individual items.