Ive done like 10 or so, which compared to others is only a small amount of modding, but I like bolting more than screws, idk why.
This guide should give you the info you need.
https://wiki.geekhack.org/index.php?title=Modifications:IBM_Model_M:Nut_and_Bolt_ModOnly things I would say, is while you have it apart, make sure you clean as deep as you can, because its a lot easier to do when you have it disassembled.
I normally do a warm bath for the cases and plate, then use a magic eraser to get all the scuffs and grime to a minimum.
I also use rubbing alcohol on cotton, to wipe down the membrane connector.
Finally, when you drill your holes, if you have a soldering iron, it makes it easy to make the holes clean.
The problem is there is a flashing ring of plastic that gets pushed up so you want to clip the excess down.
Do this part before cleaning, so that you get any loose clippings off the plate.
Best of luck!