I have a SST120 powerhead that I cannot find any serial# on...

Have been asked to locate the "welsh plug" and send numbers on this to Mercury to get build specs, but I cannot locate this plug eigther

I know where the serial# should be but there are only a large "175" engraving as seen on the pic:
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In the buttom of same side of the block, these numbers are shown:
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No numbers on top:
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Any assistance is highly appreciated!