>>921>He claims that they seek to draw a distinction between the theory of Marx and that of Engels.
Lukacs points out some differences between Marx and Engels in History and Class Consciousness
), for example:
>The statements of Marx and Engels on this point could hardly be more explicit. “Dialectics thereby reduced itself to the science of the general laws of motion – both in the external world and in the thought of man – two sets of laws which are identical in substance” (Engels).  Marx formulated it even more precisely. “In the study of economic categories, as in the case of every historical and social science, it must be borne in mind that … the categories are therefore but forms of being, conditions of existence ….”  If this meaning of dialectical method is obscured, dialectics must inevitably begin to look like a superfluous additive, a mere ornament of Marxist ‘sociology’ or ‘economics’. Even worse, it will appear as an obstacle to the ‘sober’, ‘impartial’ study of the ‘facts’, as an empty construct in whose name Marxism does violence to the facts.
<end notes: 6. _A Contribution to the Critique of Political Economy_ , (my italics). It is of the first importance to realise that the method is limited here to the realms of history and society. The misunderstandings that arise from Engels’ account of dialectics can in the main be put down to the fact that Engels – following Hegel’s mistaken lead – extended the method to apply also to nature. However, the crucial determinants of dialectics – the interaction of subject and object, the unity of theory and practice, the historical changes in the reality underlying the categories as the root cause of changes in thought, etc. – are absent from our knowledge of nature. Unfortunately it is not possible to undertake a detailed analysis of these questions here.
The other work I see mentioned (although I haven't read it) is Marx and Engels: The Intellectual Relationship
by Terrell Carver. I couldn't find a PDF of the book, but I have attached a review that should give you enough info to decide whether you want to read it or not. For what it's worth, it seems that Carver is somewhat of an Engels scholar. He published a book called Engels Before Marx
this year (https://www.palgrave.com/gp/book/9783030423704
Other than that I found a paper called Engels as Interpreter of Marx's Economics
, by Christopher J. Arthur:>This paper is concerned with Engels's work on Marx's critique of political economy. As is the case in general, Engels was originally taken as a reliable guide to Marx's work in this area; but the claim has been made that Engels's views as a commentator and popularizer are to be rejected, and that, in the editorial work Engels did on Marx's Capital, he abused (consciously or unconsciously) the trust Marx placed in him as the literary executor of the Marxian legacy. While the main interest of the paper lies in its consideration of Engels's interpretation of Marx's method, I shall first consider the charges pertaining to his work as Marx's literary executor.
>Before considering such charges it is worth noting that the habit of taking Marx and Engels as one person is so deeply ingrained from earlier times2 that traces of it survived in places until very recently. As a prime example of this tradition let us take the well-known textbook by M.C. Howard and J.E. King on The political economy of Marx, which appeared in 1975. Treating of what they assume is Marx's 'logical-historical method', they give passages as if they quote from Marx (e.g. 'in history … development as a whole proceeds from the most simple to the most complex relations') when the passages in question are really the work of Engels!3 They are from a review Engels wrote in 1859 of Marx's Contribution to the Critique of Political Economy. (I deal with it extensively below.)