$750 - $1250+ (or more) depending on shape. There are a lot of little odds and ends that are usually missing or missed when removing from the car, that can help to drive price. Complete V8 systems are worth more than L6 systems.
I agree with Southbays2s on the odd and ends. You didn't mention if the condenser and dryer are also included. Good original condensers are really hard to find. What appear to be good hoses frequently aren't and need replacing. If everything is truly there and able to be used, I'd say up to $1500.
It is still in the car and complete this a 2 owner 1 family car with 55,000 original miles I am the 2nd owner the first was my aunt, it has the original brackets and ramhorn for nova exhaust manifold date code for a 1966 vehicle i am looking to customize the car so i plan to go with a vintage air system so i guess if i have it removed, seal everything and keep all the parts in a crate i guess it could be worth something after all
If the system has never been touched and is still charged, it is running R-12 refrigerant. R-12 has been "banned" (probably varies by state) for over 20 years. It has value. Freon does not degrade and can be recovered with the right equipment. There is a process for system evacuation and depressurization. A trained A/C tech should know how to evacuate and seal the system so internal damage does not occur to sensitive parts. Contaminants - moisture and dirt - can wreak havoc inside A/C system components. All systems have different guidelines, the original GM shop manuals have all kinds of A/C info.