The only way you're going to know if they will work is by knowing the off-set of each, in general Boxsters can be out-fitted with wheels having up to a 4" lip so that is not a way to determine proper fitment.
I would say from my experience these are NOT factory wheels but they DO have the sport design spoke style optioned on the 996 original 2-pc. by BBS.
Get the off-set info and I'll be able to help you find out if they will fit. The only info you provided was the tire size which will not help.
Let us know,
Below is a photo of the original 2-pc. Sport Design by BBS
