Does the display say LOC?
Looking at the face of your GM Delco radio, hold down the preset buttons 1&4 or 2&3 for approximately 10 seconds. The radio display changes from "LOC" to a three-digit number. Write this number down.
A. Don't take too long, fifteen seconds max before the next step.
Press the AM/FM button. The radio display changes to another three-digit number. Write this number to the right of the first one.
Post the numbers back here and I can get the code for you.
Below is kind of a generic method I am not sure if it works on your radio but give it a try and see if it does I will look for your particular procedure in the meantime.
Turn the ignition ON (The radio displays LOC) Use the MN and HR buttons to enter the code MN will enter the last two and the HR will enter the first two.Press the AM/FM button.