I can't directly answer your question, I have a SS fence extension but it looks nothing like this. From looking at the picture, it must be the same extrusion as the 520 fence. It even has the cutaway and holes for mounting the outfeed end clamp, which it clearly does not have and would have no use for. A fence extension with less complicated mounting might be easier to make than this one. It is not completely clear how the SS version of this mounts other than the T-nuts, though I'm sure someone here can tell you. It involves standoffs and some "reverse thread" parts, so I think you tighten it from the gap between the fences. And end-to end extension with T-nuts? That sounds flimsy and looks crooked in the picture.
Consider repairing your fence with new parts instead. 520 fences seem to command a good price on eBay, and there are occasions when having more than one is useful.
