I can't find out much about the Telex 235 duplication system, but Telex did make quite a few duplication systems, even into the cassette era.
Telex consumed Magnecord and Viking, 2 earlier names in reel to reel technology. I have an example of each of their machines.
This set up looks to be solid state, so probably 70s era. One picture shows a switch on one of the transports for 15 / 7 1/2, but I noticed that there are only 2 channels of electronics in the little sub module rack. They AFAIK always duplicated both sides at once, so if it were 1/4 track stereo their should be four channels of electronics. It also looks as if there are only 4 head connections in one picture. Perhaps it was set up for 2 track (1/2 track) mono both sides. In which case it would also do 2 track stereo. (Same head configuration.)
So, if nothing else, it would be a source of rugged decks with 2 track heads. I am still pretty sure by the size of it that 10.5" reels would not fit, but not absolutely certain. It looks like a standard transport that they might have used in a lot of configurations from logging recorders to a full machine with electronics for radio stations perhaps.
With regard to your common mandrel duplicator technology, that sort of thing was used also (I think) in film optical printers or synchronized editing for multiple camera takes with stacks of film (or tape) running in parallel on the same spindles.
One of the more interesting machines I have is a Bell RT360 which allows duplication in real time 1:1 of a tape by means of extra reel turntables located outboard of the ones on the deck. This also allowed the use of 10.5" reels. You threaded the tape to be duplicated on the deck, but through a special set of guides only around the playback head, then the tape to be recorded to goes on the outboard turntables, over the erase and record heads as normal, then under a tab to shield it from the play head then both go out through the single capstan and pinch roller to their respective take up reels! It works. I have tried it.
A picture...
http://reel2reeltexas.com/vinListBD.html