Bought an MC28 engine from Japan. It was rough and well used but the pistons look new and clearance is perfect. Just noticed that they do not have the pins in the ring grooves to stop the rings turning in the grooves. The rings still do not turn in the grooves for some, reason, not sure what is preventing it. I don't know the origin of the pistons, they have no marks. Am I correct in assuming these pistons need to be replaced? Don't want to be snagging rings on the ports

I think you've answered your own question. If you have any doubts it's worth replacing with genuine Honda parts
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Why do things simply when you can complicate them

Yeah, I was just hoping someone might say it was OK, they are all like that. I have never bought so many parts that turned out to be junk as I have for this project.