To get inside you have to remove the security screws and the screws that hold the power supply to the bottom cover. Then you have to remove the knobs, nuts and screws to remove the main board. There is one screw hidden under the reverb board.
The new sliders were a little shorter than the old ones so I had to mount them above the board as can be seen in the following picture:
Then there was another problem. The new controls did not work at all! They are stereo controls and the old ones were mono controls. So there needs to be two jumpers installed on the bottom of the mixer to make it work. Those jumpers are shown in the following drawing:
Here is a picture of the jumpers on the back side of the main board.