The reconstruction was probably done from Bach's "Trauer-Ode" (Lass, Fuerstin, lass noch einen Strahl) BWV 198 / BCG 34. For more information look into: G. A. Theill, "Die Markuspassion von Joh. Seb. Bach (BWV 247): Entstehung - Vergessen - Wiederentdeckung - Rekonstruktion" (Steinfeld, 1981) The book includes also the facsimile of Trauer-ode. Let me know if you come across an English translation. Hope it helps. Pawel Kotla