Let's not start a "I've been doing X longer I'm smarter than you" battle. If you haven't done the actual swap, you are merely assuming it will fit. And we all know what happens when you assume.
Can you provide concrete evidence? I'd certainly hate to sell someone an axle only to find out it doesn't fit. And if it requires modifying the axle it's simply not a bolt up swap. Not everyone has the access or ability to weld.
As far as I know, the FJ 3rd will fit, however the locker will require a couple of holes drilled into the diff (?) to accommodate the wiring, etc. Not something I'd have a regular mechanic do, but it shouldn't be too expensive to work out with an experienced offroad shop.