Convert/close conventional fireplace to ceramic thimble?

[JoeOxfordCT]

Hi, first post in years. Just bought a 1978 house with a conventional brick/masonary fireplace. I have attached several pictures from the hearth project on our last house with one picture showing the current fireplace in the new house. We plan to convert the existing fireplace to be like what we had in our last house where the hearth is on the floor and there's just a ceramic thimble coming out of the wall. However, the old house was built like that with no firebox. It does have a cleanout in the basement as well.
I'm having the same mason I used to do the stone veneer at the old house come take a look at the new project. I just want to know what would be the best way to convert/remove the existing damper, connect (ceramic) piping to the existing cleanout in the firebox floor, and close up the opening so that just the ceramic thimble is protruding from the hearth wall like our last house.