If you're also contemplating going with something new for the height channels-- instead of repurposing some of your existing speakers-- then I'd definitely recommend either of the SVS Elevation series if they're available where you live.
The angled drivers and included brackets make them pretty versatile (they're fairly easy to mount on the ceiling, or up high on the wall).
No problem! BTW both the Ultra and Prime series actually use the same mounting bracket as far as I can tell. There's a separate insert that slides into the bracket to anchor the speaker and keep it from sliding out of the keyhole slots when mounted in either location.
https://cdn.shopify.com/s/files/1/0921/3560/files/Prime_Elevation_Ceiling_Block.pdf?v=1594238287
I've got three sets of Prime Elevations mounted high on the wall in my setup, but they all came with those inserts packed into the box.
EDIT: apparently the Ultra version uses a magnetic ceiling block, versus the rigid rubber one that the Prime Elevation uses, but the end result should be the same with either one.