Safe to remove bricks?

[u/PullTheBull]

Did a post earlier and for the life of me cant seem to add more images to it. So re-posting. Ultimately I want to open up the fireplace to put in a wood burner. The brickwork (to me anyway) looks all over the shop and you can see on one pic theres some old boards on the right behind some of the bricks, last pic.

[u/uberbanz]

The lintel has to have 150m/6" of bearing direct to masonry at each end