I'll offer this - for model year 86, the US-spec 420SEL and 560SEL have seemingly identical exhaust manifolds but the part numbers are different. Even the exhaust manifold gaskets have different part numbers. I guess port size is different.

Between the US-spec 84 500SEL and 86 560SEL the exhaust manifold part numbers are different but the exhaust manifold gasket part numbers are the same.

Sixto
95 S420
87 300SDL