Do you want to keep the muzzle brake or ever use it again? If so do not do what I am about to tell you!
Put your barreled action in a fixture and then into a vice. heat up the muzzle break with a torch. After about a minute or so of heat stick a good sized bar in the ports of the muzzle brake, tap the bar both ways a few time with a heavy rubber mallet then unscrew it. Has always worked for me and 90% of the time never damages the muzzle brake.
Thats actually what I was thinking, about the vice and all. Cant really get a 'good size rod' in there cuz theres not much room between the ports. And I'd like the brake intact when I'm done.
Wonder if a couple of strap wrenches (one on the barrel and one on the brake) would work...
It's a pretty small circumference for a strap wrench to get a good bite on it. I'd heat it up with a torch (preferably something low temp like propane, I wouldn't go after it with acetylene) and use the rods through the ports. If you're patient you won't hurt it.
One thing I would try first and it is easy to see if they used Loc-tite or Rocksett. Get a bucket of hot water and soak the break/end of barrel in the hot water for 5 min. Rocksett will not come loose with heat but will soften in a few minutes when exposed to water and hot water really speeds it up. We do it all the time here at SureFire and the adapters come off easy. Rocksett is used more often on barrels since it will not breakdown due to heat where Loc-tite does. Just a suggestion.