Jeff,
You are correct with Cappellano’s quote but in Finazzer and Riccio’s Italian artillery of WW2, on page 60, they have an endnote stating that it is controversial as to whether the 75/13 was used in North Africa. It also states that Pignato’s book L’obice 75/13 does not mention Nort Africa. However, they cite Storia dell’artigliera Italiana (No author), pages 600 and 601 stating that some pieces served with 8th Army Corps Artillery Regiment and with the Trento Division during the battle of El Alamein. The pictures shown in Finazzer and Riccio‘s book show the 73/13 in other theatres of war being conveyed on animals or pulled by animals. The text does mention that tests were conducted with army tractors and in particular the Fiat OCI 708 CM mountain tractor.
David, not sure if this helps you!
Bob