Kind of busy, but here's the section on moral realism. There's also the conclusion which you should read, even if you can't get to the whole thing.
iv. Marx’s seemingly relativist statements in this area are not, in fact, what many have taken them to be. They are statements not of moral relativism but rather, as we may call this, of moral realism. That standards of right are, for him, sociologically grounded or determined means that the norms people believe in and live by will be powerfully influenced by the nature of their society, their class position in it, and so on.
It means, more particularly, that what standards of right can actually be implemented effectively and secured — this is constrained by the economic structure and resources of the given society. It does not mean that the standards to be used in evaluating or assessing a society must necessarily also be constrained by the same economic configuration; that the only valid criteria of assessment are those actually prevalent, those harmonious with the mode of production. Marx’s assertion that right cannot be ‘higher than the economic structure’ is a case in point. Its context makes clear — that it is a realist, not a relativist, one. He first speaks of the contribution principle as an advance over capitalism, then explains why it is defective none the less, and says that the defects are inevitable, however, during the first phase of communism. Then he makes the statement in question and says, immediately afterwards, that the different conditions of a higher phase of communism will permit the implementation of the needs principle. Implanted in this context, Marx’s statement is plausibly one concerning the real prerequisites of achieving progressively higher er more advanced standards of right. It is obviously not a statement that there can be no higher or lower in this matter on account of each such standard being relative to its appropriate economic structure.
v. There is nothing at all either reformist or contrary to the cast of Marx’s thought, it is argued in addition, about a preoccupation with distribution as such. He does object to any over-restrictePost too long. Click here to view the full text.