http://geekhack.org/index.php?topic=37753.0
Sure he'll be in here soon enough to elaborate...
OK. In my original guide I cut off the tabs and worked with bolts exclusively, but I have since come to the conclusion that it was a mistake.
The "sliding force fit" is a tricky thing to accomplish, but the tabs and slots ensure that everything is properly aligned and fitting properly. Time after time people whine about how hard it is, but when I inquire I find that they tried to do it without clamps. Really, a good set of clamps makes all the difference.
Now, for the F-122, after doing several of these, my current preferred method is to add 2 bolts (#4 available in a normal hardware store) one approximately between 5 and F5, and one approximately between Enter and Up Arrow. Be sure that you avoid damaging the traces in the PCB, of course. Those 2 bolts will pull the plates together at the center of the curvature, and snug up everything else nicely.
The smaller XT and AT models probably do not need bolts, but I can't remember whether or where there is a reasonable place to install them, since I have not had either of those apart in a couple of years.