The best source for Ferdinand/Elefant is 2 books by K.Münch, Combat History of the 653th Schwere Panzerjager Abteilung and Combat History of the 654th Schwere Panzerjager Abteilung. The first is very hard to find and the last one can be found on the internet.
I do not remember having seen an Elefant without Zimm in these books, I'll check...