Sorry... just to be clear: when you say the plug is "stuck", do you mean that it's not turning, or that you can't remove it?
If it's just that you're trying to remove the plug, it looks in your last photo like you haven't yet unscrewed the tailpiece at the back of the lock: you have to depress the spring-loaded retaining pin and then unscrew the ring that's on the back of the cylinder. (This is what stops the plug from sliding out the front of the lock if you were to pull on the key.)
Just be careful not to lose either that rear pin or its spring when you finish unscrewing the ring!
Schuyler just put together an excellent
video on repinning cylinders that covers this and a bunch of other good tips.
