The 51 switch is the most difficult to remove without the key due to the thumb tab that's part of the bezel. That said, it can still be removed. You will need to have the switch in the center position and you'll need a thin piece of strong wire. Something like coat hanger wire that's a thinner gauge should do it. Insert the wire in the hole that's just below and left of the key opening. The wire, when pushed in, hits a spring loaded release that will allow the bezel and tumbler to be removed. Be careful when you pull the two halves apart as the key tabs are spring loaded and will fall out of where they belong.
If your car still has it's original door locks, they are the same as the ignition switch and if you pull one of them, any experienced locksmith can copy from it. I had to do that with my 54 and a week after having keys cut...I found the originals...
