Hi Scott,
They're Keskin KT2, which is a 1-piece copy of Speedline 3-piece rims for 911 turbo, if I'm not mistaken.
Looks great indeed, but won't recommend them. They're supposedly heavy and front offsets at 52mm are not ideal for 928s. RH makes a 3-piece version of these, which can be had with better offset, and Kerscher also makes a 3-piece version. I believe the latter can be custom made with the desired offset. Both 3-piece variants are much more expensive though.
Regards,
Erling