Am I crazy but isn't the plug located somewhere on the side there to check the level of the fluid?
I got my start messing with vehicles working for Shorty Stevens at his Esso station back in the mid 50s as a Jr. High punk. Most cars and trucks were std tranny and that plug is what we used to check the level and add fluid; same thing with the rearend. Now I'm to lazy to drive a stick shift and have “chickened” out to automatics.

~Jim