Back in the day, I had a lock smith make a replacement ignition/door key. He took a blank key, shined it up the top edge that came in contact with the tumblers with steel wool. Put the key in a vice grip and put it in the passenger side door lock. He rocked it back a forth until the tumblers marked the key with their location. He used a triangular file to indent each position. Polished the blank again and repeated the operation. When the tumblers quit scratching the blank, that notch was right. In ten minutes, he had a key that worked. I followed him to his shop and he used the key he made to determine the nearest code for the key, made the code key up and I was set. This was on my 1974 Satellite.
He used the passenger lock because it is the least used. He made a code key as the crude one he made would have unduly wore out the tumblers since it had real rough edges.
I have had success doing this myself to remove the ignition cylinder. Once that was out, replaced the cylinder and door locks.
Craig