I have all of the specs for the adapter available in a PDF that another ADVR converted to a usable and attractive drawing... if you want it send me a PM.
**NOTE** I had to machine the caliper mounting "ears" to remove 0.0625". This moves the caliper to be approximatley centered in on the rotor... you should do your own measurements for this one!
**EDIT added 03/17/2008***
Member HPMGUY is producing the adapter that is mentioned below. Please send him a PM or email if you are interested in one... the plans are below for any "do-it-yourselfers".... Guy's work is first rate **end edit***
And machining the word "Nissin" off of the caliper is optional.... now if I could just figure out the CNC mill to add "BMW" to the caliper I'd be set...