Hi - I'm having the EXACT same issue with my '56. I have the ignition switch out. I removed the wires from each post (3/8" socket for the nuts), noting which wires go where.
No luck rapping and lubing and probing with a pick. I can't depress the release pin on the side of the ignition switch body either. Nobody has said it yet, still, but it must be necessary to turn the key in order to depress that side pin, to remove the cylinder. One YouTube suggested drilling out the cylinder (could then maybe use a screwdriver to start!) but replacing both the switch and cylinder seems easiest at this point, around $20 each per quick google. Hate to have 3 different keys, so maybe the new cylinder could be rekeyed.
What happened: I had noticed the ignition key getting a little harder to insert, but today I accidentally tried the trunk key first, and when I realized my mistake the correct key would no longer go all the way in.
There is actually another post for a 57 that says you need to turn the key or if no key use a punch(!), which seems like a risk of damage to the switch. Best advice on that thread is probably to take the switch assembly to a good locksmith.