You have to drill out the existing holes just barely bigger than the captive nut sleeve, cant remember off the top of my head the drill bit I used. Then there is a small lip left inside. I used a 1/2" chamfered reamer from the backside to take out most of the lip to allow the nut to move when its loosened. In my case with the 362/400 cover its thinner than the nut needs it to be so I added a copper washer between the head of the nut and the cover to space the sleeve down in the hole before I crimped them permanently. I actually just used a spare bar stud in a vice to crimp the nuts, and didnt but the tool stihl sells. If you aren't very comfortable/ capable with drilling accurately and straight I would not attempt this. Not sure what a 461 cover costs but the large 362/ 400 is about $100 if you mess up its trash.