#1 Please do not turn this thread into a "don't mount over fireplace". There is already a thread for that. I am doing this for a friend who has already mounted it .

What I have research and cannot find a answer to is how to hide the power and cables in older homes. Every thread I read talks about space behind the brick or wall and from my limited experience, newer homes it looks pretty easy. But homes built 1970's and older it seems it's solid brick from floor to roof with. Am I wrong or missing something?

No, you aren't missing anything. It is customary to veneer directly to the masonry unit structure with the stone or brick facing. There is no void behind this, and really no raceway to find to hide the cables. You'd need to run them in a metal or plastic raceway, and then hide the run with additional trims when it hits the mantle. Wiremold Corp. is the first stop for the raceway, but your going to need to get creative for the way you run them for them to have any aesthetics at all.