The other challenge is, even if you adapt the calipers to fit, unless it also includes converting to Boxster rotors, you will again, have heat soak issues as the larger calipers will overwhelm the smaller rotors.
As someone who ran 951 brakes on his SC for a while, what is prompting you to make the change? My upgrade was a mixture of success and annoyance.. yes, better pad management during a 3 day de.. but can't say overall braking was any better over "stock". Had I kept the car, I was contemplating a conversion back to 3.2 Carrera calipers and rotors.
imho, I am not sure, in the long run, it is the "better" upgrade choice out there. 930 conversion or simply "big reds" with 17" wheels might be a better choice in the long run.
Might check out these guys for ideas as well:
http://www.vehiclecraft.com/