When I pulled apart the keyboard I took the top plate and just used a sharpie to mark the screw/standoff locations.

I did not bother with all the other support standoffs that dont require screws. I may 3d print some if I decide I want to make this even lower profile.

Standoffs are 6/32 threaded heat inserts I repurposed, normally I use them for 3d printed projects when I need a secure attachment point. For now they are secured both top and bottom with 6/32 low profile screws like what you would attach a hard drive with. I counter sunk and threaded the holes on the plate to make sure they are secure and dont rattle.

Yes I had a bunch of O rings I got for a build and ended up not liking so I reused them here to create some "soft" pressure to keep the PCB from just grinding away on the standoffs. If I decide to go the 3d printed standoff route so I can drop the PCB down to the very edge of the plate for a lower profile I may keep the rings to have a stiff but forgiving connection to the plate.

Yes they are the Keychron low profile caps, they required some modification to install on my K4v2 as it is a normal keyboard and not a LP one with the LP switches. I had to use an exacto knife to shave the inside of the longer keys so the stabilizers would insert and hold. You can see a little of the crud left over in the bottom picture on the left. If you have a cherry style stabilizer and want to get this or a similar set you will probably need to do the same sort of thing otherwise the plastic will be too tight and split.

if you are struggling to get standoffs in the right spot I would suggest either tracing the top plate or the PCB. The PCB still has small alignment holes for the screw-less standoffs on my board so its easy enough to place them. Otherwise get out your calipers and measure, measure, measure, because there is no really good way to get the numbers into CAD/Fusion other than doing the work.