What did the rings look like from #1 ?
That piston looks like it has had a hot spot on it or a lack of lubrication causing it to grab. If the rings were jammed it could do that. How deep is that scoring in bore #1 ? Do you think a light hone will remove 95% of it?
Be careful using emery cloth to clean pistons. It can scratch them & damage them.
If you have some solvent based paint stripper try that.
Ideally you would get all that carbon out of those grooves in the pistons.
As to reusing piston #1, If you are able to hone the bore, I would try & get a good second hand piston from a blown motor. Normally there is still a few good pistons even after a major failure. I dont like the scare on the side at all. Others may have had luck with using pistons like that.
I would use #1 piston as a paper weight!

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1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
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