The last 3 rifles I've built have used keys - they do take some time, but get quicker as you develop a process. Taylor's method is spot on, and I use virtually the same process. Drill your holes undersized, chip them away slightly (just to break up the fiber between them), and then use an undersized iron to burn your way through from each side, meeting in the middle. If you've sized the iron right, you should have minimal cleanup to do with a file just to make sure the slot is uniform through and through. It's easiest to do all of this while the stock is still square, but trimmed so there's no extra width on either side of the barrel. The burn mark will look bad initially, but when shaped you'll have a clean slot. Because you have a lot more wood to pass through, it's best to leave the keys pretty tight - you can always loosen them up a smidge when the stock is shaped. Hope this helps,
-Eric