You won't need to change your factory BDL bottom metal. The Wyatts CFE-9 has a step in the back of the box to allow it to sit over top the back end of the bottom metal slightly. The back end of the action magazine mortise will need to be milled out and the bolt stop modified. I've not seen the need to open the ejection/loading port for the RUM cartridge. The factory opening will eject a empty cartridge just fine. A loaded round however it will not. You would need to push your bolt release and pretty much remove the bolt to get a loaded round out. I've found that to not be too big of an inconvenience as your typically not in a big rush to get a live round out as you would an empty. I also recommend loading the CFE mag boxes from the bottom. You can load 1 into the chamber, close the bolt, flip the rifle over and drop 2 more into the mag box from the bottom. Trying to load from the top typically will scar up your brass trying to push it through the feed lips. Withe the CFE-9 in a HS stock you will also need to slightly open up the web between the magazine box opening and trigger opening. It's best to have the whole rifle in hand to ensure everything fits, clears and functions as it should. I do several of Wyatt mag box modifications each year. For a Wyatts CFE-9 box and action modification I get $150 plus return shipping.