The hole is not the one for the master cylinder cylinder, it is located exactly in the center of the floor board right behind the gear shift.
I have figured it out !!! The answer is ALL OF THE ABOVE.
However I did find a practical use for this "hole in the floor". Last night I drained what little lube oil was remaining in the transmission since the last time it was filled (probably 30 years ago) I found that a 3/4" hose will fit nicely into the transmission fill hole and extended it up through the "hole in the floor". I then placed a funnel in the top of the hose and wired the funnel to the "E" brake handle. Then proceeded to fill the transmission, no muss no fuss.
