If the wheel is only sticking out by 4mm (0.16") with no load on the suspension (on a jack/jackstands), they will probably camber-in enough (even on an IRS car) to clear the fenders when the car is on the ground. Don't put too wide of a tire on and you should be alright. I run 215/55-16's on my 16x7 ET40 Boxster rims and they look good.
You'll need to clearance the suspension stop on the chassis and you may also have to clearance a springplate bolt or two...or the tire will hit them.
If you put the 16x6 ET50 wheels on back of a stock IRS car you'd want ~18mm spacers, you may want a little less since you've got the 944 brakes
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