I have a subpanel of machined aluminum manufactured by Steinair when they did my panel. It had pilot holes for the throttle, mixture, park brake and cabin heat. First step was to fit the subpanel to mount to the panel frame under the middle of the main panel. This will use 3 #8 screws with nuts on top of the panel frame. Next step was to drill out the control cable mount holes to the proper sizes, (.75" for throttle and mixture, and 3/8" for park brake and cabin heat.