While the clutch release shafts A-7510-C and AA-7510 used in the three and four speed transmissions look very much alike, there is a slight difference in the shafts and it is very important not to mix or confuse them.
On the A-7510-C shaft the pin holes are located directly on the center line of the shaft. On the AA-7510 one of the pin holes are located 10 degrees off the center line of the shaft. (See Fig. 1016.)
If a three speed transmission release shaft were installed in a four speed transmission or vice versa it would be impossible to move the clutch pedal far enough to release the clutch.