Cup II's (I don't have any experience w/ Cup I's) look very similar and as long as someone purchases the correct set, they'd bolt right up with no spacers needed.
Front and rear offsets for the majority of Cup II's are 55mm. Some made for the 928 and 968 have a 65mm offset.
Cup II fronts are either 17x7x55mm or 17x7.5x65mm. Rears are 17x9x55mm.
There are a few other weird Cup II sizes, but the 7" front and 9" rear are the most common and cheapest and would slide right on a 986 and look great.
These are Cup II's on my 928 project.
I found an image of a 986 w/ Cup II's but they're kinda hard to define being painted black. I posted the picture larger mostly so you can see detail on the wheels, but also because I know it annoys a few clowns and critics on here.