Not sure. I think it may have been the right eye, but don't quote me.

Like I said, the deciding factor could be how the film was shot. The Universal 3-D rig was a parallel rig like so:

image

Meaning emulsion would be towards the screen when printed, rather than the normal emulsion away from screen.

Some of the camera rigs were in an "L" configuration like such:

image

And therefore, the left eye is the primary negative used for various "flat" prints because its orientation is "normal" rather than flipped.