Middle Seat Shoulder Belt Retrofit

[gskurka]

I need shoulder belts for the middle seat in my 1986 GMC Suburban. The kids have graduated to booster seats and now I must have shoulder belts. The GMC dealer stated "they can't sell me a shoulder belt for an '86, since it wasn't original equipment". I know later models had the shoulder belts, but I'm not sure of the year they were factory installed. Does anyone know if the attachment points should have been installed and what part number I should order?

I would also be interested in used belts if they're in good condition. The interior on this burb is blue. Thanks for your help in advance.