S4 engine with S5 housings

[Pettersen]

I'm almost done building my semi pp engine, it has s5 rotors and rotor housing, everyhing else is S4 T2.

Since i'm new to rotarys still, i didn't realy know or think that there where differences between the housing, but now i know that the spark plugs are moved slightly and i'm not shure how to tackle it.

Is it something i need to consider when setting the timing, or can it simply be done with changing the settings in the PFC ?