Something like this had my thoughts for awhile:
http://www.sdp-si.com/web/html/newprdshafts2.htm its a spline to keyway adapter, but they get pricey, then to buy a pulley. Probably just as much as if i just went and had a pulley made.
This was the biggest dilemma i ran into during the build. Actually still looking for a good smaller pulley. Alot of the Mercedes tuners ran into this problem and had to resort to a smaller crank shaft pulley.
Though, i just thought of this, my SC is driven off a pulley i have attached to my PS pump, i Could just find another smaller pulley that would run fit my PS pump and not touch the PS pulley.