I'm not sure about original-equipment heads, but if it's ever been rebuilt, it's possible seat inserts were installed. A competent machinist should be able to determine if seat inserts have been fitted, and if they're in good shape. Other sources of metallic debris in the cylinder might be pieces of a piston ring that had been broken while installing the pistons. The only way to be absolutely sure nothing is damaged is to do a complete teardown, including pulling the pistons and rods. If the rings don't have more than a few miles on them, and aren't damaged, it should be OK to reinstall them. They might have to "break-in" again, but that shouldn't cause any long-lasting problems. Good luck!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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