This is driver side frame rail, the middle frame piece is common to both sides I think.
Also for sale:
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Aftermarket, JDM, USDM - upgrades/replacement parts - http://www.son240sx.org/forums/showthread.php?t=38573
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Brakes - Upgrade And Replacement Parts - http://www.son240sx.org/forums/showthread.php?t=38586