A few pictures to clarify
1: On the right the old cluster with the back plate off, on the left the replacement. Note the 4 pins on the right side, these connect to the bi metallic strip on the back plate. The old cluster does not have the bi metallic strip.
2: Sorry for the poor quality. On top is the bi metallic spring, and below you can just make out the 4 copper plates which connect to the 4 pins on the above picture.
3: The outside of the backplate. It is clearly original
It appears that the bi metallic strip controls the fuel gauge and empty tank light, which do not work now. Why are they connected with the bi metallic strip?