There are numerous books by Marković and Stojanović and at least one by Gajo Petrović in English, as well as several essays by these and other Praxis philosophers in English in print and on the Internet, not to mention the secondary literature. (See for example the Praxis Group in the Marxists Internet Archive.) I just want to mention these books:
Crocker, David A. Praxis and Democratic Socialism: The Critical Social Theory of Marković and Stojanovic. Atlantic Highlands, NJ: Humanities Press; Brighton, Sussex: Harvester Press, 1983.The Praxis School is compared with related philosophical dissidents in Poland, Hungary, and Czechoslovakia in:
Marxist Humanism and Praxis, edited, with translations, by Gerson S. Sher. Buffalo, NY: Prometheus Books, 1978.
Sher, Gerson S. Praxis: Marxist Criticism and Dissent in Socialist Yugoslavia. Bloomington: Indiana University Press, 1977.
Satterwhite, James H. Varieties of Marxist Humanism: Philosophical Revision in Postwar Eastern Europe. Pittsburgh: University of Pittsburgh Press, 1992. (Series in Russian and East European Studies; no. 17)But back to the philosophical interaction between Marković and Kurtz. I refer now to an interesting volume which contains the contributions itemized below:
Humanist Ethics: Dialogue on Basics, edited by Morris B. Storer. Buffalo, NY: Prometheus Books, 1980.
Comment by Mihailo Marković on Kurtz [“Does Humanism Have an Ethic of Responsibility?”], pp. 31-33.When I am able to secure the full text, I will report in greater detail.
Reply by Paul Kurtz to Marković, pp. 33-35.
“Historical Praxis as the Ground of Morality” by Mihailo Marković , pp. 36-50.
Comment by Paul Kurtz on Marković Article, pp. 51-54.
Reply by Marković, pp. 54-57.
Crocker, who incorporates analytical philosophy into his analysis of Marković and Stojanović, devotes some space to a critique of “Historical Praxis as the Ground of Morality.” In a couple of places he mentions disagreement between Marković and Kurtz:
It must be admitted that Marković appears to have two minds about what this “appeal to history” amounts to. On the one hand, he says that three normative attitudes to the course of history are possible and that if soft procedures fail to bring consensus, then “discrepancy in value judgments cannot be overcome” (HP 40). Moreover, in responding to Paul Kurtz, who takes Marković to be trying to deduce the Ought of praxis from the Is and Was of history.  Marković says, “It [Praxis] cannot be derived from any factual judgment (which would constitute the naturalistic fallacy) but it is linked with a basic factual assumption—'Praxis is enente of history,' or more clearly: ‘Praxis is the specific necessary condition of all historical development’” (HP 57). On the other hand, both in HP proper and in his response to Kurtz, Marković appears to have something close to hard justificatory intentions. In the latter Marković claims that ethical pluralism gives rise to the need for “a foundation of ethical values” (HP 55). That is, because “various groups or individuals have genuine moral convictions with implicit claims to universal validity,” and because “these convictions are different or even incompatible,” one must ask oneself, “What is the ground on which his implicit claim to universal validity rests?” (HP 55). [p. 214]. . . with this footnote:
44. Kurtz charges, “Marković seems to be committing one form of the naturalistic fallacy by defining as intrinsically ‘good’ one aspect of human history (praxis) and then reading that into the process as a ground for his preferences.” “Comment,” in Humanist Ethics: Dialogue on Basics, ed. Morris B. Storer (Buffalo, N.Y.: Prometheus Books, 1980), p. 52. [p. 223]And here is the other comment:
Because people are used to a dichotomous either‑or (or to compromise positions), they (like Paul Kurtz) are likely to construe Marković’s procedures in terms of the dichotomy [of relativism and absolutism/dogmatism]. To the hard justificationist and skeptic, Markovic’s approach will look like no justification. To the absolutist, Markovic’s soft procedures will appear relativistic. After all, Marković does not demonstrate praxis and proceeds on the assumption that there is no way to get conclusive proof that one ethical outlook should hold for all people at all times. Moreover, what else is relativism but an unhappy compromise that weds skepticism to the view that each moral outlook is true (for its group)? And do not Marković’s procedures entail that any group (or individual) that employs them will emerge with what is ethical truth for it (him and/or her)? [p. 219]These are, of course, only fragments of Crocker's presentation. In Storer's volume itself there are main essays by both Kurtz and Marković, and exchanges between the two on both of them. I will save further commentary for a future post.