Help with Wheel/Tire fit on 1990 964 C4

[BrownGill]

I finally settled on a set of wheels. I am a total novice. I have learned everything I can possibly learn from the forums on wheels and tires. There are so many threads on this subject. I am sorry to post another one.

I made a deal on the wheel/tire combo below. Do you think they will fit on my 1990 964 C4 (obviously narrow body) without spacers? The offsets are so close. Also, do you think the tires will work without rolling wheel wells? I figure I am going to have to change out the 285's for something smaller. Lastly, how important is it for a C4 to have the same total diameter on the front and back wheels + tires? Thank you for your help.

Fronts: 993.362.134.06
7.5 x 18 ET 50
Tires 225/40

Backs: 993.362.138.01
9 x 18 ET 52
Tires 285/30