Stereo Compositing with different cameras

Hello all. I am researching for a project I am doing next year.

To keep it brief and to the point I want to use a stereo rig in order to composite the image from a modified camera over the top of my normal shooting image. Camera A is a Blackmagic Cinema camera, but due to the nature of the camera I can't modify it In the way that I need to. So we are looking into modifying a hacked GH2.

—There would be no interaxial separation. I would simply be overlaying the two images, masking out the areas I want shown by the modified camera in post.

—Neither cameras have Genlock so I would have to LANC the two together, but I realise there will be shutter drift very quickly.

—Whilst both cameras are m4/3 mount the GH2 has a slightly larger sensor. This will affect my field of view obviously, but not my depth of field. Technically all I am doing is using more of the image circle by a crop factor of 0.3. Same lenses will be used on both cameras.

—The modified camera image will look very different to the standard camera

—I am at no point utilising the whole frame with the modified camera. Only the areas I am masking out in post.

So I am desperately looking for opinions on what potential issues I might have and whether this experiment will work with the option I detailed above. I don't really want to shoot with two GH2 fir these shots but if this is the only way to do it I may have to.

Thanks for your time.

Tim