I have checked my model to see how it fits Handly and it looks like it may take some work to get it in place. I have a couple of questions about your design choices.
My model used the Java model as reference and thus has IParent and IOpenable as separate intefaces. Do you have any special reason not to use the same separation, or was it just not necessary?
My model uses also collections instead of arrays, which makes the data easier to process, without having to convert to arrays every time, only when interfacing with the Eclipse APIs. Are the arrays a "must"?