The salt is sucking moisture out of the air, without removing all the flesh I don't know how you could fix that, if you have a taxidermist near you If I were you I would talk to one or two for advice. So far as the antlers go, you could make a fake skull out of plaster of Paris with the antlers inserted up to the pedicel like they were on the skull. You might want to drill a hole in the middle of the antler and epoxy a bolt in the hole to give the plaster of Paris something to hold onto. After they are mounted into the plaster you can cover the plaster with leather and no one but you would know they were not on a skull. You could then mount the fake skull on a plaque, you can buy those kits cheaply.