Harness is different on 68, so yours will need to come out at some point.  I'm not sure what dealer has to read monitor.  
Just for a comparison, depending on condition of chains, sprockets, belts, pickup and number of bales your 467  should be worth between 10 and 12 thousand with some extra credit for new parts.  We just traded a 2002 567 and 15,000+ bales for a 2008 568 with 11,000+ bales (568 gone through shop with new chains and sprockets and repairs on pickup and belts) for $6000.  568 with 5000 bales would have been $15000 trade.  I don't know how much the silage special adds to the value of the 458.