Fireplace fitting

Hi, I'm looking to put in a cast iron fireplace in the upstairs bedroom. The fireplace has been breeze blocked in and where I an looking to cut a hole out of the breeze blocks only to fit the fireplaces back in.
This will only be for decoractive purposes and not for fire use. I'm wondering if cutting out is suitable or if i need to first locate if there is a lintel in place? Pics attached.

Hi, you could use an angle grinder or Stihl saw etc to cut out just the correct size or to create far less dust you could stitch drill the blocks by drilling lots of holes all the way around the perimeter you want to remove and then knock out the blocks. The problem you then have is that the thin slips of blocks to the left, right and top of the hole you make are very likely to become loose as they look to be only 4 or 5 inches wide on either side and may not survive the drilling/cutting and hammering etc. Best option is to remove what has been breeze blocked in and rebuild it leaving the correct size cavity to fit your fireplace.

Thanks DAZB.
I like the idea of stitch drilling to reduce dust. The blocks go up another foot and a half at least above and where a large concern I have in removing them all is all the plaster work after and lintel needs. I made a hole (covered by the A4 paper on the pic) to check at breeze block top end to the brick start if a lintel was visible but couldn't see one? Not sure if would be found further up though.
I guess I'm hoping and wondering if I only cut the size shown this would not adversly affect the structural integrity above?

for a start the blocked flue needs sweepin an ventin no matter what happens next.

remove the plaster to expose the original opening. ie where block meets brick.
keep goin up until you expose the old lintel or brick arch.
a lump hammer will easily smash the central block back an you can then work at nocking out the remainder in pieces to reveal the original brick openin.

Thanks bobasd,
Do i need this swept if not using for a fire?
The backing is only small as per pic, and the hole size is small for that to fit into the fire place recess (gaps in the cast iron as seen will be repaired/ filled). This was why I only wanted to remove and create a hole the size shown. My worry was if by cutting this hole size out, if any support above would be compromised?