can't help you with those. I though they might be for mounting the mufflers on a 996 (i.e., common cam cover used for both engines) but, from the images shown here they are not:
Pelican Technical Article: Boxster Engine Conversion Project - 986 Boxster (1997-04) - 987 Boxster (2005-08)
i did note that the bracket appears to use the cam cover bolts to fasten itself. the Porsche procedure for tightening these requires that they get done in a certain order, so you might want to check that out.
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