Can you see something I can't?

Presuming the clearance is around 0.04mm (you did measure it, didn't you?) I'd run that.

As stated on this forum about a million times the corrct piston to the barrel (i.e. a-b, b-no mark, c-d) is no guarantee of correct clearance.
This is the result of running an unmarked piston in a B barrel. That (unmarked in B) is correct but the B barrel has been plated, it's not stamped up, but it's the wrong height (replaters tend to remove some deck height) and quite clearly a bit tight.

It ran fine, didn't seize,the barrel is barely marked and both that barrel and piston will get used again, probably not togeather though.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread