I GOT IT OUT! And in one piece too!
l let it bathe in some WD 40 again while I had lunch. Then I spent some time playing with it and my friends; the small c clamp, and the nuts & bolts, & tape that I was using as blocking. I did manage to get to slide a bit. But then I couldn't secure the barrel in the clamp any more. It kept slipping and rotating instead of pushing the sight.
I tried the hammer and punch (really a bolt) again and it came out. Not right out, but it did move with each tap. I think it only took about a dozen taps this time, unlike the plethora of wacks I gave it unsuccessfully before.
I think moving and stressing the blade with the clamp helped the oil penetrate into the joint. I suspect the same could have been accomplished with just the WD 40 and a pair of pliers gripping the blade and stressing it back and forth for a while.
"Sometimes I pretend to be normal, but it's boring and I go back to being me."
"You might as well be yourself, people wont like you anyway."
"Tres verbo dictom"