Change offered meta boxes based on custom post type hierarchy level

I’ve been trying to find a way to use two custom post types (with a 1:n relationship) as a child-parent relationship, but I’m getting nowhere without my work-arounds; I need the “type B” items to have a parent assigned from “type A” items.

I cannot use a taxonomy for this… there are specific restraints that just make it not possible. I would also like the menu structure to look nice.

So my new method is this… is it possible to offer specific meta boxes based on hierarchy level. So in other words, all items would be the same post type, and the top-level items would have its own unique fields, and the second level would have its own unique fields. (third level or more would not be used)