Hello George,
thanks for your personal e-mail, I hope you don't mind me replying to it here!
The 2000 Rostyles will fit on 3500 studs (and vice versa, of course) the only difference being ½" in rim width. The 2000 type are 5J and the 3500 5½J. What I don't know for sure is where the extra half inch is inserted, i.e on the outside, inside or equi-distant. However, no problem with fouling of the wheel arches or suspension components but what I had heard, and have mentioned on this site some time ago was the tale (may be allagorical!) of a P6 owner who had P5(B) Rostyles fitted and when he crashed and made an insurance claim the company refused to pay out as they discovered the "wrong" wheel on the car when inspected by a loss-adjuster.
I think the important point to make is TELL YOUR INSURANCE COMPANY whatever you do and, in my opinion, you won't fall foul of the insurance companies if you fit 3500 Rostyles to a 2000 model but I wouldn't recommend fitting 2000 wheels to a 3500 model!
Hope this helps.
Regards, John.