They are aftermarket upper and lower control arms.
They will let you change camber and probably caster and tighten up the suspension a bit by replacing the rubber bushes that would more likely than not be worn out by now.
Sprinters come stock with adjustable castor rods (they call them tension rods in Japan). However if you want pillow ball or even more adjustment or more bling then something like the picture may be needed.
So a sprinter could "support" them, there's just not such a big need for aftermarket ones. On the other hand S13 ones aren't factory adjustable, so bigger market for them.