R P Casey Concludes - At Least Some Marcionites Used a Diatessaron

" ... We must, therefore, reckon in the East with a form of Marcionism which found the popularity of Tatian's harmony too great to be set aside. That this was not true of all Syrian Marcionites appears from the Syriac spurium on the Parables extant in an Armenian version and attributed to St. Ephraim. It may be that a Marcionite version of the Diatessaron was issued to meet the need of Eznik's group, but it is at least certain that the Diatessaron and not Marcion's much mutilated version of Luke was the starting point." [R. Casey, “The Armenian Marcionites and the Diatessaron,” JBL 57 (1938) p. 192]