help finding Marx quotes (and so on)

Now I'm translating an article series (by Finn-Enotaevsky) about Marx's theory of value, and the author doesn't always give exact references:

Finn

The concept of socially necessary labour was not discovered Marx, nor by Ricardo, like Engels says in Anti-Dühring. 'Socially-necessary labour time' was already put forward in the first half of the eighteenth century by an anonymous classic, which Marx himself indicates.

So where exactly did Marx credit this anonymous classic?

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In 1927 a draft notebook by Marx was published in the USSR:

Marx, Karl 1927, 'Iz chernovoj tetradi K. Marksa' [From a Draft Notebook of K. Marx], Letopisi marksizma, No. 4: 56–62.

What was its content? It seems only mentioned in White, James D. 2001, 'Nikolai Sieber and Karl Marx' in Marx's Capital and Capitalism; Markets in a Socialist Alternative, ed. Zarembka, Paul, Amsterdam: JAI Press.

White seems to be the only one to reference this notebook and he translates a part of it:

Among Marx's published notes there is reference only to the first of Sieber's
articles in Znanie. It contains the sole point of criticism Marx found to make
of the article in question. This concerned Sieber's defence of Marx against Karl
Rössler, a German reviewer of Das Kapital, who had demanded to know why
it should be that 'the food in the stomach of a worker should be the source of
surplus value, whereas the food eaten by a horse or an ox should not'. To this
Sieber had replied that the subject of Marx's investigation had been human
society and not the society of domestic animals; therefore it had been concerned
only with the kind of surplus value produced by human beings. On this expla-
nation Marx commented:

The answer, which Sieber does not find, is that because in the one case the food produces
human labour power (people), and in the other - not. The value of things is nothing other
than the relation in which people are to each other, one which they have as the expression
of expended human labour power. Mr Rössler obviously thinks: if a horse works longer
than is necessary for the production of its (labour power) horse-power, then it creates value
just as a worker would who worked 12 instead of 6 hours. The same could be said of any
machine (Marx, 1927, p. 61).

This error, as it happened, was one that Sieber would later correct in articles
written in Marx's defence.

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So any idea if this draft notebook is already published in a MEGA volume?