"pushing hard" actually works. I first ran a putty knife (Michael Bush said I might need to use a tool to help me) along both sides of the foundation to break the connection to the bottom (narrow) bar. Then I sort of bent the bottom bar as I pushed and lo and behold the foundation popped out - some more pushing followed and the rest of the foundation freed up from the frame and I had empty frames for my SC starter strips.
Here are pictures:
I'm taking my own picture, so I am holding both the putty knife and the hammer in one hand, the camera in the other - you realize that in real life I held the putty knife in one hand and hammered with the other.
Having run the putty knife on both sides of the foundation and having hammered in the center with the hammer against the putty knife against the foundation, I pushed hard and the foundation popped out of the frame. A little more pushing and the foundation was out of there.
I put the popped out large cell drawn comb foundation into a bag to take to my bee club to give to anyone there who would like drawn comb from good bees:
Linda T - grateful for all of Michael's suggestions!