That's a non-stock housing!

You can grind a lip on the outside of the merc manifold, and smooth that step on the inside to be able to use a silicone (or cheap rubber) connector. This is a perfect excuse to buy a w115 intake

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment