Look inside the trunk lid at your RPO label. You will see the RPO codes that make up your car in alphabetical order. You will have either CJ2 or C60 but not both.
CJ2 is automatic air, C60 is manual air.
Once you have that info call or e-mail:

Morad Parts Company
3455 W. 140th (service road)
Cleveland, Ohio 44111

P (216) 671-3736
F (216) 671-8406

sales@MoradPartsCompany.com

Hours: M-F 9AM-6:30PM
Weekend pickup by appointment.

and they will hook you up. I had an automatic actuator go bad a couple of years ago and they fixed me up with a used one for $40 or so and it's still working today. Morad Parts specializes in W-body GM cars so they have what you need.
Once you get the part it's held on with three screws; figure 20 minute fix.