Boxsters would normally wear 7.5 x 18 front rims with ET50 offset, so those wheels are...
going to sit 5mm further into the wheelarch than OE wheels, which may cause rubbing/fouling on suspension components or rubbing on full lock - could be rectified with 4mm spacers
going to be very prone to kerbing as there will be virtually no tyrewall bulge to protect the rim edge
Boxster Rears are normally 9 x 18 with ET52 - you are not a mile of with those rims, but it will be very tight ft against the rear suspension arms and the brake line as the rim will be 2mm further into the arch (Porsche recommend cable tieing the brake line on some earlier cars). Again you may be better with a very thin spacer (i've seen some advertised at 3mm), although i do know of US owners using 285mm wide rear tyres which would potentially pose more of a fitment challenge than those rims you list.
They are obviously not Porsche OE rims as they are not sizes for water cooled Porsche model - bear in mind aftermarket / copy wheels can be considerably heaver and of poor cast quality. Plenty of non Porsche wheels being used of course, just be careful.
Try before you buy i guess is the only definitive answer, they aren'e a mile off but decent quality spacers aren't cheap if you need them.
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