It's possible they're from a different engine altogether and as such the first five digits are different. But out of the 7M's family, that number would be for 0.50 over sized pistons (yes, 0.50mm). I can't find anything else and nothing pertaining to the MKIII Supra or any North American vehicles. If you research it and find more I'd love to know. I'd speculate about it being a superseding p/n if not for the fact that it's already taken.
BTW - Toyota liked that bore... there are a number of pistons which will fit the 7M but aren't meant to.
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