Most of the Super Ds came without Grafloks, but they can be added by machining a Graflok back down to fit into the existing rotating back. You do not lose the rotating feature. One has to shim up the ground glass about 1.2mm to compensate for the slight change in distance, but infinity focus is preserved as the native focus has a bit of over travel.
If you supply the back and the camera, then I think a service charge ought to be about $3-400 to do this, as it will take about 4-5 hours for a nice neat job. You could also do it yourself.
I have one that I did at http://imagemeister.blogspot.com that you can look at.