[PaulE]

I can't help you with part numbers, but I also have a 2003 Boxster S. A few years back I bought 5 stock lug bolts from Itsnotanova (Woody) when he was still in the used Boxster parts business to get rid of my lock bolts. He didn't ask me what year or size bolts I needed, the ones he sent me were the same length as the ones on my car. I have both 17 inch and 18 inch OEM wheels and no spacers, the lug bolts work with both of them just fine. The length of the bolt shaft to the ball washer thing is just under 30 mm. If your rear lug bolts are too long, I think they will interfere with the parking brake mechanism inside the hat of the disk brake rotor, and that will be a big mess for you. Here is a picture of one of my stock lug bolts. Hope this is helpful.