All the screws are out?
You want to have a person helping if possible, to make sure it doesn't fall
out. But once the screws are out, it's just a matter of working it out of there. A putty knife or something similar to gently pry helps.
Since it's been in there for 30+ years, it's pretty well stuck in place. Shouldn't take too
much persuasion to get it to separate, though.