You might want to consider a Garmin G5 based autopilot for your RV-4.
Yes, the separate components cost a bit more, but they also offer so much more. There is absolutely no better autopilot ergonomics available than the GMC 307 which provides dedicated buttons and knobs for all the important functions.
It really is better to not have the attitude and air data sensors buried in an autopilot box with no ability for the pilot to see what the autopilot believes to be the pitch/roll/vertical speed/altitude/airspeed/etc. With the G5 you always see the attitude and air data information that is being used by the autopilot to fly the plane.
Additionally, you have a flight director that can be turned on with the FD button should you wish to hand fly the plane using this guidance with the autopilot servos disengaged. If you are hand flying using the flight director and want to turn the plane back over to the autopilot, just press the AP button. It doesn't get any easier.
If you install a second G5 instrument, and the primary G5 fails, you still get to fly home with the autopilot since the second G5 will take over and provide the autopilot function when it goes into backup reversion and becomes the primary flight instrument.
Let us know if you have questions.