This mod was the main reason I picked up these sets. I had no plans to buy it until i saw this post.
I just finished the mod and love it. It was very straight forward and the only extra pieces I needed were a few 1x3 bricks for the middle arches in the pit, and a lot of dark bluish gray plates for the palace extension, and I ended up using about 6-8 1x6 light bluish gray bricks for the palace floor. The 2nd rancor pit should provide everything else you need. I used random bricks for floor support, but they aren't needed. The rancor pit had extras.
I'm not sure i understood the reason for pulling the tan bricks from the floor spacing. I didn't need any. I removed the tower from its base and it was a direct drop in to the new floor.
I didn't realize the OP raised the rancor pit by 2 bricks. I didn't do this and it's quite cramped. I recommend anyone planning to do this mod to raise the pit height.