S1/S2 VN V6 mix&mtching?

[Manual Calais]

What problems may you encounter when mixing and matching say s1 block wit s2 heads/inlet manifold or the other way around?

[NPreston]

I have S1 with S2 heads, you will need to block two holes on the inlet face of the heads with welsh plugs and a bit of work on the inlet manifold where the welsh plugs fit if you are going to use a S1 inlet manifold on the S2 heads.

[Manual Calais]

wat about s2inlet and heads, then just block the two holes?