katharinemn, this setup does not allow for the ideal placement of the TV. The ideal location is actually above the fireplace. And by using TV tilting hardware, you can lower the TV to the perfect viewing height. With this option I would recommend TVCoverUps.
Framed art(including your own) or mirror adds to the room's decor with the hidden TV and Entertainment Consoles beneath.
See how EASY it really is:

Is it really appropriate for you to try and sell your stuff on my Houzz page? There is no way that you could fit an appropriate sized TV over that fireplace.

TV Coverups - wow, what a lousy suggestion. Placing a TV over the fireplace puts it well above comfortable viewing height. So, you may be proud of your gadget, but it DOES place the TV is the worst of locations. You acknowledge this by then suggesting that the TV be secured to hardware that has to both extend several inches to clear a mantel AND lower the TV as well to a "perfect viewing height" - that sounds like a wonderfully Rube Goldberg device that homeowners will love using every night.

By the way, you may also want to mention in your sales pitch that the mantel has to be clear of photos, vases etc otherwise they interfere with your device's operation and interfere with viewing the TV...