It is a summer, near holiday, weekend, asking a question about some specific cars that are not common. Also, many modelers are outside persuing their other interests. Me I just came in from unloading hay.
Anyhow, unfortunately I am unfamiliar with the set of cars yor are asking about, so can't be of much help there. From the circus train I remember seeing and ones in photos, there are a variety of specialty cars, many longer than the "normal" of the day, usually painted up in the circuses color scheme.
As for motive power, I don't believe they had their own, but were hauled by the ower of the trackage they were going over. A large train often was double headed with whatever steam power was available from the local rr. Don't need to add locos, use what you have.
Hope someone sees this that has or is familiar with the cars you are asking about as it sounds like a fun project. My original Lionel set, with extras, came with several wooden circus cars, which I never finished putting together. Still have them.
Good luck,
Richard