There's no way an FS9 scenery like that will ever run in FSX.
The missing support for it in the Addon Manager is one reason, but the main thing is converting it to FSX it's very complex, because we don't just "patch" the sceneries to work from FS9 to FSX, but we always remade them as natively as possible in FSX, so they'll perform good (fps for sceneries just patched to run in FSX are really bad).
Pisa is not something we are considering to redo in FSX because, as for all the italian sceneries we made, it didn't do very well commercially.