I have identified the engine on this page: https://trainspo.com/model/2401/ It is in fact engine number 7535 of class Zs. I photographed it, complete with this number on the bufferbeam on 16.4.1994. Gauge notation: 1000 mm.
@ter I have a book in my library called 'Schmalspurbahnen in Griechenland' by Hans-Bernhard Schönborn (1997). On page 237 I have found confirmation of your suggestion that this class is called Delta Iota, meaning Di. Ten engines were built 1951 by Breda, Italy.
@ter I can see your point. I will investigate further. When you look at page 2 of 3 of this thread, you can see that on May 21, 2016 user GAZKGK refers to the locomotives as Delta Alpha. So I am not yet convinced. It should be two letters, in any event.