Dr. Wolff, in reading your books so far I've come to understand how Marx looked at any community or work force as one group that is actually producing the surplus, and one that isn't. This is very clear, what is not clear to me is how most of us these days fit into this picture. I am an Engineer in the Electronics sector, and as you may know this type of work does require you to actually "produce" the goods that eventually generate the surplus, in fact Engineers layout the "blueprints" of how electronic products are designed, used, manufactured, and so on, but we don't work on the assembly lines that physically produce these products. So, in your assessment where do Engineers fit into Marx's view of labor, surplus producing vs. non-surplus producing?
Marx's value categories are ways of thinking about the economy; they do not map one on one with existing entities in an economy. An engineer - a category developed outside of Marxian value theory - is examined through the lens of Marxian value theory. To do that entails, for example, asking and answering such questions as: (1) does this engineer engage in labor that produces a commodity (good or service); (2) does this engineer produce a surplus, i.e. engage in "surplus" as well as "necessary" labor as Marx defines these terms in Capital; (3) does this engineer receive an income that is a distributed share of the surplus appropriated from other workers. Depending on the answers to such and further, derivative questions, a Marxian "analysis" of the concept "engineer" emerges. Likely this analysis would make distinctions among "engineers" who are producers of surplus and those who are not, among those who received a distributed share of other workers' surpluses and those who do not, and so on.
It is unlikely that you would find a one-to-one mapping/correlation between Marxian value categories and the job description categories that have grown up within and for a capitalist economic system.
Such a Marxian value analysis of engineers might have practical political value by identifying which engineers occupy class positions akin to other surplus-producing workers and which do not; this could and should inform union and party organizing approaches to such engineers. And so forth. In short, Marxian analysis seeks to connect any object of its analyses (e.g. "engineers") to issues of class, exploitation, class differences and class conflicts. Value theory does that, whereas alternative theoretical approaches do not. The latter have other political and theoretical goals and thus generate different analytical outcomes.