Machined out the bottom of the stock for my new bottom metal using a dremel and metal files. Also had to drill out the old pillars and put in bigger ones. Filled in my sloppy edges with bondo.
It was semi hard because the entire inside of that B&C stock is a solid block of aluminum so it's fairly slow going. I spent probably two hours on it, going back and forth between hand files and the dremel. I found the sandpaper bits removed the most metal the fastest, but also wore out fast. If you are not pillar bedding, I wouldn't try it as it would be nearly impossible to get the internal surfaces perfectly square with a dremel.
If you have patience and at least some experience using hand grinders, you should be fine.