Oh yes, and regarding the green R2 unit, there is another shot of R2-D2 earlier in the scene where the red unit is still in the background, only not as obvious. Unfortunately Luke and C3P0 walk in front of the camera, but if you could take the section of the clear shot and extend it to the same length as the original segment you want to replace (it's only about ~ 30 frames long) I think that would be a better option.