We have a mid-sixties home with a brick/masonry fireplace not unlike this. I’m about to embark on a project to put bookcases on either side of it and it occurs to me scope creep is in order. It’d be nice to raise the fireplace about 18”. Is that within the realm of DIY? What’s involved? Does the entire chimney have to be replaced? Any online or book references you can direct me to? If I was to pay someone, what would it cost in SoCal?