The suggestion about putting the Gulbransen stack into a  freezer
overnight and then jumping on it (or smacking it in just the
right spot) may not be so far-fetched. I have a friend who quite
successfully dismantled a Duo-Art expression box with precisely
that method, as per instructions in an old AMICA Technicalities
bulletin. The old hide glue gets pretty brittle at around zero
degrees Fahrenheit. If the piano plate is cracked, and
Gulbransens have such an ornery reputation anyway, what have you
got to lose?

Cheers

Doug Rhodes