1977 GMC Savanah Motorhome - Ignition dashmount removal

I'm trying to replace the cylinder in my motor home ignition. The previous owner broke the key off in the ignition and it is unretreivable. I have the back plug off of the cylinder. There is an outer ring that retains the entire component onto the from of the dash, and the cylinder is recessed towards the engine. There is a toothpick sized pinhole on the face of the cylinder where the key is to be inserted. behind the plastic dash, on the 'barrel' of the cylinder there is a hole half the size of a pencil eraser and inside that hole (which is recessed) you can see the inner ignition barrel. The barrel has a small flange that I have shifted slightly making the the inner barrel move counter clockwise - the motion that would typically stop the engine. I have tried everything to remove it... and I'm stuck!!! Help me!!!!

Mat