I am not sure this would be a good idea, not because Soundsmith isn't excellent, but because the Decca stylus mounting system is unlike anyother, as you well know. With most cartridges, the stylus rake angle is about 15 degrees toward the pivot of the arm. With Deccas, its the opposite direction, as you can easily see. With a conical stylus, that's no big deal. But with a line contact stylus, its not likely to sound good at all, since the line will be contacting across groove modulations. I know what the later Deccas use line contact stylii, and I don't know how they manage it, whether they have changed the angle, or mounted the stylus differently, but a simple replacement might be disasterous.
Possibly Soundsmith has a method to deal with this issue -- I'd contact them about it.