Goal # 1 was to remove top brick so we could (a) have a mantle above FP and (b) so we can easily hide speaker wires behind (new)crown molding for surround sound system.
Goal #2 was to convert wood burning FP into Gas FP w/blower. To do this, we had to make opening bigger by removing top layer of bricks on hearth because it was above the bottom level of FP.
Goal #3 to cover the old brick with some type of tile and finish with white wood mantle for a clean updated look.

Lessons leaned so far:
Use a chisel hooked up to a air compressor. Made it very easy. And have a spray bottle of water to keep dust down a bit.
Use eye protection, mask and have a plan to dispose of the mortor and place to stack bricks.
Protect flooring, cover everything! We did not cover enough and dust got everywhere downstairs - even two rooms away! So, plastic off the area too.

Picture of getting started:

This one I call Pondering ...

This one is "almost done .. need to remove top layer of bottom hearth for gas insert opening.

This is a close-up look of filler behind the "pop-out". We found narrow cinder blocks. The rubble is part of a cender block we smashed with a hammer to get things flush with the height we want.

This is a close up of what is under the top layer of bricks under hearth, it seems to be cement filler. The lines you see are not bricks under, but markings from the bricks that were once there.

This is where we are at today .. now what?

So this is where we are at today. The opening is perfect for the insert. The wall after repairs and painting will be ready for crown molding. We are thinking we want to remove the "pop-out" to make it easier to build a mantle on. We are not sure how to get the metal support piece out yet.

I hope this helps some of you who have been wondering what's behind your FP bricks!