[BB_TX]

Don - When I made the cabinet insert to install the TV, I made it about 1/2" less in width and height than the opening. But when I went to insert it, I could not get it it because of the wood trim around my slide would not allow me to slide it straight in and it would not go in at an angle. No way could I wiggle it and get it in. So I had to take it apart and cut the width down by 3/4". That just barely cleared the trim. Then I needed a filler strip (1" x 2") down the left side to fill in that space. Our floor plans are very similar so you would probably have the same clearance problem. No cables on that side.
Another slight problem I had was that some wires did come in at the very bottom right of the opening and ran across the bottom of the open space to the back left corner. No slack to move them. So I had to raise the bottom of the insert about 3/4" so the wires could run under the insert. You can see the wires in the 3rd picture. Also wires/cables come up thru the rear bottom of the space, but I only made the insert about 12" deep so it does not interfer with those wires/cables.
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The big square hole in the back is an opening thru to the toilet room that allowed access to the rear of the TV. Has a plastic cover removable from inside the toilet room. Mine had a heavy sliding metal mounting structure to hold the TV (the square black object on the bottom in the 3rd picture). But you had to access the back of it to press a release handle to allow the TV to slide out.
Now the opening provides an easy way to access the cables behind the TV in case I need to add or change any.
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And in the first picture, you can see the fireplace is at the bottom below the middle set of doors with the mantle below those doors. It is still there. The TV is above those doors.
I have another slide show for the fireplace install.
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I did no cabinet cutting/modifications for either install.