I've been using the original 240mm bed mount design on both of my Kossel LP,s since a rebuilt them in 2022 and am grateful to the original designer Petieken. One of the beds on my Kossels is an Ultrabase and the other printer had the standard heated bed with the Build-Tak type adhesive sticker, both native 240mm diameter. This latter sticker eventually got damaged when an over-enthusiastically adhered PETG print tore a chunk out of it. and I decided to replace it with a magnetic PEI flexible plate from Energetic. One of the irritations since fitting, was due to the bed just sitting on top of the mounts and any attempt to remove the magnetic sheet usually entailed the bed lifting out of the mountings too, so I set about fixing it.
The modification requires the three pre-drilled holes in the bed, to be tapped out at M4 thread. Three M4 x 8mm countersunk screws are then screwed from beneath the bed to secure the bed mounts to the heated bed. The mounts are then secured to the printer frame in the normal way. This allows beds with the factory fitted Ultrabase to still be secured down, even though you might not fit a magnetic surface. Once done, a quick Delta calibration and a nozzle Z offset check and you're done. Hope folk find it useful.