The Fine Things are Always Hand Made
Your speaker is held to the front panel by wood screws (I can see one in your photo), not to the floorboard. Remove the screws holding the speaker basket to the baffle board (front board) and try again.
The silver painted wood base is there to raise the speaker height enough so the speaker basket is just above the cabinet floor. That silver wood piece should not normally be secured to the cabinet floor. Leave the 4 screw/nuts alone.
Owners manual says only to secure the speaker with 4 wood screws to the front baffle board. Look for and remove them and the speaker should be free for removal. It is heavy.
There were just 2 of those wood screws on the bottom, but the wood base was stuck to floor. A previous owner had painted the cabinet blue and stuck the speaker in before the paint dried. Anyway, after a little careful prying all is well. The cone is good.
Stuck to paint was my second guess!
Thanks for the help. Now to find a glass dial cover.
Pretty much every size you could want.