Absolutely. What is efficient is not at all the same as what is equitable or moral.

But, I think it's far too often a knee-jerk reaction that people conceptualize problems of this sort as falling into that realm of the tug of war between morality and efficiency. But I don't think it's that straightforward at all.

Depends on what you're view of what social justice is (and there are tomes of information and approaches out there offering different conceptions of it). But what if your view accorded well with, or implied that an individual's right to life (in the literal sense, not in the abortion theme-loaded sense), was the most sacred right that social institutions should protect? Then one could argue that the "most just" thing institutions could do is help develop mechanisms to simply save the most lives. That is, regardless of social class, creed, gender, etc. And a market for organs is probably the best way to maximize the number of lives saved.

I'm not necessarily arguing that this is my personal feel about social justice, but I'm saying that it's a compelling point that can't be dismissed so easily.