Hi. I have these wheels on my 944 S2. I can tell you that the fronts are 7j not 7.5j. I've seen this on a few websites and I'm not sure where it comes from, but it's possible that 7.5j wheel was made for the 928.
Part numbers I can't tell you for sure (I don't have the car at the moment) but I seem to remember the rear 9 number started with 928 and the front was 944. Indicating again that the front on a 928 was a different size.
One thing I notice on mine is that they do not have the numbers either side of the valve. This is usually an indication that they are replicas but I put it down to them being made by Fuchs and that they are forged. The rear (inside) of the wheels are clearly marked by the production process (the hammer marks) but the front is not. My guess is that something had to be done to the front of the wheels to remove the hammer marks and that also meant that the numbers couldn't be on the front.
My wheels have unfortunately been painted and don't have their original anodised finish. If you're a perfectionist you'll probably want the original finish, but I'm not sure how many of these wheels there around to choose from. So far I haven't found anywhere that can return them to the original finish.
Tyre sizes on mine (7 and 9) are 225/50 and 245/45, I believe this were the porsche advised sizes.
http://www.944silverrose.co.uk/technicial-information.htmlWhen I got my tyres it was only really Continental doing both sizes for front and rear. Since then Pirelli have started to make them, but I've not found anyone selling them. I've contacted Pirelli to confirm and they should be available to anyone wanting them so it's probably an email or phone call to the reseller as none seem to have them on their websites.
I hope someone will jump in and correct any of this if it is nonsense.