I tinkered around with it and got it off - take a punch and knock out the pin holding the bar in place in the rear sight. Depress the retaining spring and unscrew the front. It takes a little while because the spring keeps slipping, and is annoying, but it'll come off eventually.
I put the pin back in and am using it and the threaded nub as an interim sight.
To get the rear sight base off, I'm thinking the old whack it with a hammer/attack with dremel idea will do the job.