That's a trickier one because of space limitations and working around the existing holes. You need to keep the signal split through the output, so you need separate tone control as well. Look at your cavity and see if you can handle 2 volume, 2 filter, and 2 Q plus a stereo output jack, plus a stereo/mono switch. It may require enlarging the cavity, at least undercutting but it may even need a proper enlargement with a new backplate.
Study the space first and imagine the control layout and how that would work for you.