I agree with the guys that say it's a 20-25K car in today's market depending on what a close inspection reveals. One thing I would point out that hasn't been discussed, is how to increase value with little money spent. I think with some elbow grease you can help the value. De-ricky racer the car. Un-hot rod it. Pull the engine, paint it, detail the carbs, put in correct or at least black plugs wire and stock coil back on it, stock valve covers and rad hoses. Those little things will give it a lot of eye appeal, and it's mainly labor. You mentioned you had new carpet, definitely install it. Re-dye anything that needs it. Fix the exhaust tips. Make it look the part of a super nice car with just a color change. The way it looks now, is tired and worn out. Not that that's bad, but it impacts perception which impacts price. Then, put it out there for sale or trade.
I think you get the most money out of a trade, whether you trade up or down. With those things fixed, you could ask for 30K and nego down and still probably come out ahead. Local cruise-ins are your best bet. Find a guy that just "likes" the car. Dealers and guys on the various boards are typically very savvy and won't pay top dollar. You could even say they want something for nothing, but in today's world the guy with 30K cash to drop on a car is still a tough find.
Personally, I like the car. I'd polish it and drive the snot out it.