Look, this will be a guide/guess, and I assume these wagons are marked up for somewhere in the 1924-28 era (it will be important just to check these dates on the wagons - get your magnifying glass out !).
In Germany at least, the route at this time looks like being Strasbourg - Kehl - Karlsruhe - Pforzheim - Stuttgart - Crailsheim - Nurnberg - Marktredwitz - Schirnding - Cheb. In the text it says that the two extra cars were added at Stuttgart (did these come from somewhere else, I wonder?).
So cutting this up into the logical Laenderbahn sectors, you could say that it was likely that a former Baden Pacific IVf or IVh could be used from Kehl to Pforzheim (or possibly Stuttgart, I'm not sure how picky they were at State borders in the 1920's). I think most of the IVh class were stationed at Offenburg after delivery so this would be logical.
For a prestige train like this, they'd want to use their best engines, so for the Wuerttemberg part, I'd say an 18.1 would be appropriate, possibly piloted by a T5 (75.0) for the initial stage out of Stuttgart. The 18.1 would stay with the train to Crailsheim, where likely a 18.4 or 18.5 would be the train engine. Probably anything from series a-f or h-k might be suitable - series k was delivered in 1923 or so. I have all the dates for these but I can't lay my fingers on the exact book at the moment, so I may change this.
The 18.4 or 18.5 would then likely take the train to Marktredwitz (possibly a change in Nurnberg). You could have engines with Bavarian numbers to 1926 when they were renumbered - so there are heaps of detail possibilities. It's also worth noting that three of the original series of Br 01 were delivered to Hof in 1926 as 01 005,6,7 so even these could be possible here for the run to/through Nurnberg.
These years were a time of great change : livery, numbers, nationalisation, so a lot of stuff could happen, however with this stock I reckon you want to keep it all pre-1930 maybe - and I don't know that much about earlyish Ep II. Maybe Marktredwitz to Schirnding could be a 38 even !!!
In short, there are a lot of possibilities, but they are not completely random... However, at 3.30am, unable to access my stuff for fear of waking others, it's the best I can do off the top of my head..
Interesting question, many possibilities, hope these are some ideas.