The rust looks to be a characteristic of an engine that sat for some time and got moisture at the top of a piston.
I am guessing the some of the rings were stuck?
The scoring is not on the pressure face of the pistons. Since the skirts look good, I would try to free up the tight pin and then run them. Any high spots can be cleaned down on the pistons, File, stone, sand paper, something like that.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.