If retention bracket holding screws are identical to the last photo of those instructions, then you can just push them out. They get "stuck" once you tighten screws hard enough on bracket itself. If you plan to preserve them, use soft tools to push them out, made from wood or plastic, also use corrugated cardboard underneath MB so that it would sit on a stable surface and scews would have just enough room to move.

OK, thanks SSTV2. I tried what you said using some corrugated cardboard, but all I hear when I bear down on the brass studs are the little creeks of the motherboard doing things it doesn't want to do. I really think these are fastened to the mobo in some permanent way--perhaps with an adhesive. In any case, I think I will just modify the cheap retention brackets I bought by drilling out the plastic posts and then just using the brass studs (I failed to remove) along with a nut on top of the brackets to install them that way. A bit hacky, but it should work.

Once I've successfully hammered out soldered in screws out from Dell GX1 motherboard 🤣. In your case, screws are being held only by friction, unless someone has actually glued them there, check if holes are not filled with any sort of glue, if not, it's only friction.

I looked very closely but do not see any obvious means of fastening other than just friction, so I think you're right. In fact, I've reconsidered my solution. Besides, I don't have any properly sized nuts anyway, and even if I did, it would be hard to get at them with a nut driver. I guess I'll just throw caution to the wind and push very hard. I'll do all I can to prevent the board from flexing--I'll use the cardboard again. I don't know about using a hammer, but at this point, I'm frustrated enough to use a lot more force.

Well, I tried again with the cardboard and just bore down with the handle end of a screwdriver and they pushed out just fine. Then I had some difficulty getting the new brackets in. And they don't sit flush against the board when the cpu is installed--it pushes them out a little and they lift off the mobo surface at a slight angle. But at least everything is installed now. Thanks again for your help.

Glad to hear that. Maybe you are using SECC2 CPU in original PII SECC brackets? They are not entirely compatible.

Nah, it's a Klamath based pentium 2 266. These are the brackets I installed.