I’ve got a H89 with some head work, mainly on the exhaust side. My mechanic said there was no need to port match the inlet as it would have been way to big. I have a redline twin side draught manifold. Now my q’s is should I match the manifold to the head via building up the manifold with weld or some sort of epoxy or just leaving it as is?

I personally prefer to have them match

What are the pros and cons? I was told by someone that having the lip helps with making the flow of air become more turbulent and that this is a good thing?

If you want the maximum power, make them match. Sudden steps in the pipe are bad for flow. I'd recommend doweling the manifold to the head and then port matching. Whether you add to the inlet or take off the head is up to you, just keep the transition smooth and gradual. Think 15° included angle for contractions and 10 for expansions like a venturi tube.

Ok I get the dowelling part but your last recommendation for the contractions and expansions angle. Can you explain that for me. Cheers

Ok, by contraction or expansion angle I mean the cone angle. Imagine you're using a piece cut out of a cone to join two pipes of different diameter, the cone angle is the angle between the sides of the cone. Basically you just want smooth, gradual changes in runner cross section. Steps or abrupt changes restrict the flow.