Boy that was easy! Made myself some barrel blocks out of 1 1/2" oak I had lying around. Put the barrel in a vise and got everything snugged up. Put some Kroil around the base of the brake and crush washer. After having a light lunch, I decided to put a wrench on it and give it a twist... came right off!

It's 5/8 x 24 TPI and the SAS brake threaded right on with no problems. FWIW - if your suppressor threads onto a FA/brake, you'll need to use Loctite on the FA/brake. Ask me how I know