Hi Katrina,
I think the difference is the three speed has a round opening, and the four speed has a square. The master cylinder opening is different on the ½ ton, as it is attached to the brake and clutch pedals, (closer to the center) where ¾ ton and up, the main cylinder is attached to the frame, (closer to the driver door) I have both, and I will take a look tomorrow to be sure. The most unusual would be the ¾ ton with a three speed. I have never seen that floor panel. It is kind of tricky buying one, they all look alike from afar, but they are not.
