8.75 rear end is not usually referred to as a Dana rear end, it is a Mopar rear end built under license. (It was a Dana design of the clutch system) What it is worth will depend a lot on what kind of shape it is in. By center section are you referring to the whole third member or just the sure grip section?
This rear end will be worth more to someone who already has a car with 2.94 gears. Most people doing a performance build are going to use a 3.23 or 3.55 with an automatic. Something like $350 would probably be a fair price, the killer on these things is going to be the shipping. Might want to try and sell it locally first. I memory serves me correctly, this third member has a different spline count than the later ones if the car still has keyed axles which makes its adaptability to the later years more difficult and probably more trouble that it is worth. You have a pretty specialized item here.
The axle spline count on all 8 3/4 s is the same. The pinion yoke spline count used on all 742"s and all performance aftermarket 10. The last time I sold a Center section exactly like this one I got 525.00 for it. Must have been 5 years ago. But i wrong about the 1969 and newer Sure grips 489 case. They are Borg Warners not Auburns.