Hi Jim,
The basic reference you're looking for is in Marx's letter to Dr. Kugelmann dated July 11, 1868:
"Even if there were no chapter on value in my book, the analysis of the real relationships which I give would contain the proof and demonstration of the real value relation...the mass of products corresponding to the different needs require different and quantitatively determined masses of the total labor of society. That this necessity of distributing social labor in definite proportions cannot be done away with by the particular form of social production, but can only change the form it assumes, is self-evident. No natural laws can be done away with. What can change, in changing historical circumstances, is the form in which these laws operate. And the form in which this proportional division of labor operates, in a state of society where the interconnection of social labor is manifested in the private exchange of the individual products of labor, is precisely the exchange-value of these products. The science consists precisely in working out how the law of value operates."
Shane Mage
"Thunderbolt steers all things."
Herakleitos of Ephesos, fr. 64