Linked meshes would not work for the purpose of displaying both the body torso and the shirt at the same time because for now they can only be used witin the same slot, meaning activating one would deactivate the other.
However the principle of duplicating a mesh and replacing the image path to get matching vertices and weights is good.
If chainging a mesh path is not possible due to the different shape of the torso vs the shirt image, the second best option is to create one mesh and its weights, then check the option wireframe. This will make the mesh vertices always visible and allow you to use them as a reference when creating the other mesh.
In fact, the key to avoid parts of two meshes to deform differently is to have the vertices on the portions that overlap be placed as matching as possible, and with matching weights.
When this is done, you'll see that the two parts will act as one as you wished!
