Dave:
Look here for what you will find as to identifying markings on the backside of the wheel....on the spoke area--->
http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/564841-fs-one-genuine-fuchs-7-x-16-wheel.html
If you take one of your wheels off...and get the grime off the spokes...you will see 8J x 16 if it's a 8" wide wheel. The part number will tell you if its a 911/930 pattern 8" wheel....or if its a 944/951 pattern 8" wheel which has a different offset and brings the 951 wheel "inboard" (toward the center of the car) another ~ 1/2" compared to the 911 pattern.
I thought the turbos and turbo look cars were fitted with 245/46-16 rears?. Maybe you have 7" rims with the 225's of the narrow body car on your wide-body?