Here are the mounting dimensions of our 1723 Center S speaker.
We only recommend using 2 of our own mounting brackets and mounting the speaker flat with it leaning against the back wall. We do not recommend any tilt or swivel mounts as the thread inserts are not made to sustain those much higher forces. If you need a tilt and swivel mount you can get one that clamps the speaker to better distribute the load or have a custom shelf where the speaker sits.