Marx's 1844 Manuscripts are an early attempt from him to describe the nature of labor, capital, wages, and alienation; working within a Hegelian/Feuerbachian framework; sitting unpublished until 1932 and thereafter providing a concrete link between absolute idealist philosophy and his later work with historical materialism for continental philosophers to ooh and ahh over.
There are about three different undercurrents through the manuscripts (which are often unfinished, or are missing pages, or were merely drafts). The economic parts are mostly notes on Smith/Say/Ricardo. One difference between the earlier and later manuscripts is that Marx seemed only to encounter Ricardo's notion of rent at a later date; meaning his earlier treatments of it are still vague, but he later acknowledges it as the foundation of the direct opposition between wages and profit, which Ricardo noted as well.

The chapter on alienation is one of my all-time-favorite pieces by Marx. Although it's probably slightly imprecise to say that Marx was concerned with the *injustice* of the capital relation, so much as he was interested in (what he took to be) its inevitable dynamics, which were (are?) contrary to human life. (This theme—that capital is contrary to the life of the species—is later taken up by the Italian Marxist Amadeo Bordiga, and taken to its furthest extremes by the recently departed Jacques Camatte.) To say that the *concept* of private property need be abolished is also somewhat imprecise within a Marxist frame, since concepts merely reflect material realities in the mode of production. Just some random thoughts.
Hm... I still think he's concerned with its injustices; even if the transition to communism is inevitable, it's worth speeding up... and in the 1844 Manuscripts the vibe I got was that abolition of the concept is synonymous & necessarily attending to the abolition of the material circumstances, since he's operating still at this point within Hegel. Perhaps later he distinguished between the two. What do Bordiga and Camatte say?
It's possible that his emphasis in the 1844 manuscripts is more Hegelian, I haven't done a thorough read of the text in a while. There's a famous anecdote though that he would laugh whenever people would talk about morality. Which isn't to say that he was totally unconcerned with injustice, but that part of the materialist methodology (if such a thing exists) necessitates a deflation of the ethical component of things. Bordiga is a very "traditional" reader of Marx, so he emphasizes a lot of these sorts of things, as well as writing, famously, about how "the hell of capitalism is the firm", rather than the intricacies of its administration—which, again, aligns with a materialist / structuralist critique, rather than an idealist critique which focuses on, say, the actions and attitudes of "great men". Camatte was a member of Bordiga's circles, and some time in the 60s began arguing that the proletariat could no longer function as the revolutionary subject, that they had been subsumed into the capitalist order, and that the real conflict was not a class conflict but the conflict between capital, on the one hand, and humanity on the other. Sort of like the humanist obverse to Nick Land's accelerationist coin.