It was the fact that the T981 appeared to be built on a Yashica FX-3 chassis that first got me interested in the camera and my main intention was to verify the camera's heritage. I had already seen written that it was based on the Yashica chassis and used the rangefinder from a Phenix 205. Being built on the Yashica chassis would, for me, be an advantage as I've repaired many FX-3 cameras and am very familiar with the construction and adjustments. I knew nothing about the Phenix 205 though.

Dismantling the camera soon proved the chassis was indeed a Yashica derivative. Some changes have been made to the casting but some features are clearly left over from the Yashica.

 
T981 chassis (top) compared to the Yashica FX-3 chassis (below).

The top part of this image is the T981. The small radius on the chassis doesn't need to be there. It's a left over from the Yashica chassis shown in the lower part of the image.

Most of the film advance parts are inherited from the Yashica too. Here's the underside of the T981 (top) compared to the Yashica. Note the cutout on the circular part attached to the bottom of the wind shaft. This is part of the wind lock on the Yashica but serves no purpose on the T981. Also the hole in the plate which is the hinge point for the wind lock lever in the Yashica but, again, serves no purpose in the T981.

There are, of course, a number of differences. The T981 not having a mirror box and no mirror mechanism, which in the Yashica activates the wind lock, needed a different system. And the lever activating the mirror release wasn't needed so was removed. The plate added to the front of the T981 chassis that carries the lens mount needed a cutout in the front of the chassis and this hindered the battery compartment so, as you can see above, a different battery compartment was used and it was rotated 90 degrees.

The rangefinder heritage was a little more difficult to prove as I needed a Phenix or Seagull 205 and, despite the huge number that must have been made, they are rare in the West. I did eventually find a non-working example of a Seagull 205.

T981 rangefinder (top) and Seagull rangefinder (below). Both rangefinders are 1:1 using solid prisms for the viewfinder rather than the more common lenses with a semi-silvered mirror.

Some changes were necessary to the frame mask and the method of moving it.

The T981, with interchangeable lenses, required a different method of coupling the rangefinder but the T981 (top) has clear similarities with the 205 (below).

So the T981 rangefinder is clearly based on the 205 rangefinder as suspected.

None of the above is particularly surprising as it was common practice to re-use parts from other models when designing a camera, especially the budget cameras. Given that Phenix was used to build many of these budget cameras, they would have been well used to this method of development.

Maybe of interest is the fact I managed to break the frame line mirror in my T981 while reassembling it. No problem. I took the mirror from the Seagull 205, which was identical, and fitted that in place of the broken one. Which shows there is some advantage to cameras with a long heritage. Often parts can be recovered from other models to carry out repairs.