Porsche boxster 16" wheel fitment (1303)

[MdR]

I think it will be the 944 aluminium arms that dictate what wings you'll need. I reckon you will need wider ones.
You can work out the extra track of the A arms over a standard car then minus the gain by the bigger offset rims.
Or you can simply measure across the outer faces of the 2 rear rims & compare to a standard width car.