Sending information on the lock cylinder and the ignition switch both.
Ignition Lock Cylinder Replacement - On Vehicle Removal Procedure
Push down on the allen wrench to release the tab on the lock cylinder inside the lock cylinder housing.
Important: The gears between the ignition switch and the lock cylinder housing must be in the correct position. Failure to do so will cause a misalignment of the gears in the ignition switch and the lock cylinder housing, which may result in a NO START or BATTERY DRAIN.
Ignition Switch Replacement - On Vehicle Removal Procedure
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Tighten Tighten the 2 tapping screws to 1.5 N·m (13 lb in).
That makes it much more difficult as you already know. What you will need to do, is to set the new lock cylinder in place along side the one in the column and then estimate about where the push in retainer pin is and drill a new hole in the housing so you can access the pin in the old cylinder and push it down to slide the cylinder out of the housing. If you make the hole too big the cylinder will not be a tight fit in the housing. If it is too small you will need to hog it out enough to access the pin. It is either that or replace the complete lock cylinder housing. So, either way it needs to come out and if you mess it up, you are no worse off than if you replaced the housing anyway. We have the same kind of a problem with the Cavaliers and end up replacing a lot of housings on them when the ignition lock cylinder fails. Before you start drilling, make sure the battery is up, maybe reconnect it and turn the key, then unhook the battery again. (be sure radio is in off position so it does not go to theft lock mode. Also check the shift lock solenoid and make sure the lever is all of the way in park.
Sending another page from the manual for you. Note the blue high lights will not open for you as they are GM access only. Let me know how you make out. Thanks
The automatic transmission shift lock control system is damaged.
Repair or replace the BTSI as needed. Refer to Automatic Transmission Shift Lock Control Disassemble - Off Vehicle or Automatic Transmission Shift Lock Control Assemble - Off Vehicle .
The lock cylinder housing assembly is damaged.
Replace the lock cylinder housing. Refer to Ignition Lock Cylinder Replacement - On Vehicle .
The shaft assembly is damaged.
Replace the shaft assembly. Refer to the appropriate procedure from the following list:
The ignition switch assembly is damaged.
Replace the ignition switch assembly. Refer to the appropriate procedure from the following list:
The shaft linkage adjustment is improper.
Adjust the shaft linkage adjustment. Refer to Shift Cable Adjustment or Shift Cable Adjustment in Automatic Transmission.
The rack preload spring is broken or weak.
Replace the rack preload spring.
The park lock cable is not adjusted properly.
Adjust the park lock cable. Refer to the appropriate procedure in Parking Brake from the following list:
The key is incorrect, bent, or twisted.
Replace the key. Refer to Key and Lock Cylinder Coding in General Information.
The rack is bent or broken.
Replace the rack.