These two pictures show the panel bracket (also made by Aerotronics) for the control cables mounted underneath the panel frame.  The holes in the bracket from left to right are: 
Go Around…..Throttle….Prop…..Mixture
This last picture shows the GTN750Xi mounted in the panel.  There was a fair amount of work to get the mounting tray installed the way I liked it….correct height and depth as compared to the autopilot controller and general visuals of the unit compared to the rest of the panel.  For the installation, I installed screws through the countersunk holes already in the mounting bracket, then through the instrument panel standoffs.  I had to drill a few holes in the standoffs, but the installation wasn’t very difficult…..just took some time to get right.