Thank you for your message! Here is a link to the dimension sheet - https://stonemt.net/wp-content/uploads/Englewood.9-2.jpg

We can make filler pieces that are the same color and material as the mantel, you would install those first, making them tight around the insert, then install the mantel over the top. Here is a link to our installation video - https://youtu.be/001ighgK3Sg

Thanks!