TTI 1 7/8 Headers hitting oil pan
Not applicable to your situation, BUT: My one-each Hedman header of the nominal size (1-5/8") didn't fit with my Milodon pan without some 'persuasion' to the header with a hammer.
It is also true that my Milodon pan is not shaped like yours.
It's maybe not JUST the 1-7/8" part of the equation that's a problem.