Rekey an old lock is a simple task. Making an old lock take a different key is a completely different animal. The tumbler is the issue. Chevy and GMC used different keys for ignition and door lock. If I remember correctly, and that is a big if, The door lock key has a different offset at the long groove. The one that goes along the key. You could get 2 door locks and use 2 left side buttons to key both doors. But I am not sure that you can use a single key for both door and ignition. A good locksmith may be able to reset the pins in the tumbler, and match an existing key. That would give you 2 door locks and 1 key, for the doors. Getting that key to work the ignition? I don't know.
