Tom, the studs from the wheel hub are too long and hit the back of the wheel. LPI racing won't take them back. The guy who posted that he had them on his car didn't reply to my PM.
http://www.nsxprime.com/forums/showthread.php?t=120721 <---A guy (GCNSX) says here he has them on his car.
Patty, my friend Steve (996garage) was also looking at 20mm spacers for the front wheels of his '04, and he figured it would need to be a 22-23mm spacer in order for it to work: http://www.nsxprime.com/forums/showthread.php?t=131006
The guy that posted he had the 20mm spacers on his car has a 91 with '94-'01, 16/17" wheels (according to his old posts). The 20mm spacer should work for the 16" wheels, but not for the '02+ 17" wheels.
If you can't return the spacers, you should sell them to someone who runs 16/17" stock rims. Good luck!
Mike