I do not need to provide editing from the control, just the selection (and of course filtering) mechanism.
I have not said anything about editing. If you are referring WebEditor , this is a Telerik.Cms.Web.UI attribute used to add a selector.
then when the user clicks "i'm done" the control will render this specific item. I assume i have to create a type editor whose Value property returns the content item's GUID, but how would i, for example, create a drop down list which has the title of all of the GC items in this predefined category for the user to select.
You need to create a class that inherits from WebUITypeEditor<String>. You should create a template for your WebUITypeEditor and list all items filtered by category name. Then when select the name from the RadComboBox or other control you should return in to the Value property.
If you want to use the Guid instead of the name you should inherits from WebUITypeEditor<Guid>
All the best,
the Telerik team