Exactly which Zeiss Contaflex did you inherit?
There were a number of different models made from 1953 to 1972.
You mention that it has a Zeiss 45mm f/2.8 Tessar lens, which appears to narrow it down to the earliest model I or II, both of which have non-interchangeable lenses (can't use the 135mm TriX mentions above). ORpilot's camera, shown above, appears to be one of these non-interchangeable lens models (accessory slip-on lenses were available for wide angle, tele and macro).
A Contaflex 126, which uses Kodak's type 126 "Instamatic" cartridge film and was made from 1966 to 1971, was available with a Zeiss 45mm f/2.8 Color-Pantar lens. The Contaflex 126 is clearly marked as such, right on it's pentaprism. This camera does use interchangeable lenses, unusual among 126 film cameras. Focal lengths from 25mm to 200mm were offered, but they are a completely separate series than the 35mm film Contaflex used. There
was a 135mm f/4 Tele-Tessar offered for this unusual camera (but it looks different from what TriX shows above:
https://www.pacificrimcamera.com/pp/zicontf135tes126.htm). The 135mm f/4 lens for the Contaflex 126 will not fit onto the 35mm film cameras.
The 35mm film Contaflex are more difficult to tell apart... There were nine or ten different models, but most aren't clearly labelled with a model name or number. They use interchangeable "lens heads", rather than fully interchangeable lenses. Among these, there were two camera series that don't share lens heads:
First, there were several budget/entry-level Contaflex models.... Alpha, Beta and Prima... use a lower-priced "Pantar" series of lens heads: 45mm f/2.8 , 30mm f/4 and 75mm f/4. These lens heads are not usable on any of the other Contaflex models.
Second, the higher-end models Contaflex III, IV, Rapid, Super, Super B, Super New, Super BC and S models all use "Pro-Tessar" lens heads. There were two series of those: "old" style 50mm f/2.8, 35mm f/4 and 85mm f/4, as well as "new" style 50mm f/2.8, 35mm f/3.2, 85mm f/3.2 and 115mm f/4.
These lens heads are all interchangeable. The rear elements and aperture of the lens remain permanently affixed on the camera... only the front elements are changed out. There was no 135mm lens offered for these cameras.
In fact, one of the unique things about the Contaflex is that they use a leaf shutter, instead of focal plane shutters like most other 35mm SLRs. Leaf shutters are able to sync with flash at all speeds, among other things.
Another neat thing is that it's really easy to load the film in them. The entire camera back is removed as a unit, the film is installed in it, then it's reinstalled in the camera. There was a version of the film back available that allowed safe removal mid-roll, so that film type could be changed out if needed.
There also was a stereo image attachment available for some Contaflex. I'm not entirely certain what cameras it worked on.
I wouldn't be at all surprised if the camera you inherited works fine. If it's a model with a light meter, that may not work but the camera is fully usable without it.
You might find these sites helpful for general information about Contaflex and to help identify which model you've got:
https://www.pacificrimcamera.com/pp/zicontaflexsh.htmhttps://en.wikipedia.org/wiki/Contaflex_SLRhttp://camera-wiki.org/wiki/Contaflex_(SLR)Once you know the model, you may be able to get a manual for it here:
https://www.butkus.org/chinon/zeiss_ikon.htm(Free... but donations are welcome!)
Personally I have a Contaflex Super B with two film backs, 35mm, 50mm, 85mm and 1:1 Macro lens heads.