Johnny,
I've seen your exact wheels with 17" on the back and 15" stock wheels on the front. I thought the diameter difference was too great, and very noticable. A 1" difference front to rear is much more subtle, and actually looks better than the same rim diameter all around.
Laslo Antal of Australia has a black GR4 clone with 16" and 18" rims. It was the last PI issue cover car. If you can find a picture of that Pantera in profile, you may get a better idea of what those diameters might look like together.
Michael
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