I don't agree with Engels' interpretation because 1) I don't think Marx is describing "simple commodity production" because Marx never uses that phrase 2) Engels' interpretation is essentially ahistorical, arguing IMO that value has a transhistorical existence, with previous societies giving rise to forms of value that in turn exist as a homunculus to the full-blown expression of value production with industrial capitalism.
Just doesn't work that way. That objects become commodities, were exchanged as commodities priority to the triumph of capitalism is obvious, and not the point. Marx separately discusses how such exchanges occur at the periphery of societies, where they come into contact with other societies.
But Marx's analysis of the manifestations of value in Capital is an explication of the qualities of that value that must be, can be derived only from the organization of labor-power itself as a value; the organization of labor as value-producing.
I think that is the core of Marx's discussion in the next section, section 4, on the fetishism of commodities. He states:
Political economy has indeed analysed, however incompletely, value and its magnitude, and has discovered what lies beneath these forms. But it has never once asked the question why labour is represented by the value of its product and labour time by the magnitude of that value (1).
And the footnote leads us to another brilliant discussion of the inability of economists to apprehend the social conditions underpinning value:
The value form of the product of labour is not only the most abstract, but is also the most universal form, taken by the product in bourgeois production, and stamps that production as a particular species of social production, and thereby gives it its special historical character. If then we treat this mode of production as one eternally fixed by nature for every state of society, we necessarily overlook that which is the differentia specifica of the value-form, and consequently of the commodity-form, and of its further developments, money-form, capital-form, &c.