The main case fill/check plug is visible at the lower right of your photo. The plug just ahead of the torque tube pivot is for the U joint. That one doesn't need much, just a cup or so. Fill the main case until you can reach through the hole and just barely touch the fluid with a fingertip. Filling the case all the way to the bottom of the plug hole can cause leaks due to heat expansion of the gear lube. The spinning gears splash the lube around inside the case.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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