Your truck's value also depends on the pieces involved. You said you have a 350, but what are the axles, transfer case and transmission? If it is a NAPCO upfit check with their site:
http://autos.groups.yahoo.com/group/napco4x4/ bunch of great guys with lots of knowledge. Bottom line is pretty hard to pin down, what some one is willing to pay for it would be the value at the time.