Thanks for everyone's response.

I also found some information suggesting that the larger exhaust manifold runners are used for reversion control and therefore should not be ported to be gasket matched...

The difference between my cylinder head port diameter and exhaust manifold port diameter is 3mm to 5mm.

I went back and remeasured the W116 and W123 manifold port sizes and while they appear to be the same, the overall W123 manifold volume is less and I have to agree with DeliveryValve's comment on increase velocity.