The core drills we used to use 30 years ago were large powerful drills without clutches, they had long bar screwed into the side handle thread to give you more leverage when the drill did snatch (but it still took you by surprise)
You could put a SDS bit into a chuck but if it slipped it would chew up the bit.
I would buy a 8 or 10mm masonry bit and carefully stitch drill the wall avoiding breaking through to fast and then chip the block out carefully with a hammer and chistle.
The vent kit will tidy up and slight raggedness of the hole.
I could have done the job faster than typing this
Pete