There are several good books about eclectus as well. I have them both and think they are good books. You asked a question about walnuts, almonds, etc. Eclectus parrots do not have beaks that are made to open hard nuts. Even almonds, which are generally considered to be soft shelled nuts, are too hard for most eclectus to crack open.
Walnuts are too large, and too hard.
You can encourage your bird to play with and eat almonds in the shell if you give the bird some help by cracking the shell a bit first. What we do is crack open a few almonds and let the bird eat them - that way they know there is a delicious nut inside the shell and how to pick it out of the shell. This way the nut can be a toy and food at the same time. Eclectus like walnuts, too - but not too many because they are oily nuts. Crack a walnut open and let the bird pick the nutmeat out of the shell.