@keith.sowinski the block input is to tell the underneath AutoCAD API in which drawing it has to look for those object types. A block could be an entire DWG Model Space. In this implementation of Dynamo for Civil 3D we don’t have access to multiple DWGs so the block really means the Current Document > Model Space.
As you already understood, not all the object types defined in AutoCAD and Civil 3D have been wrapped into a dedicated Dynamo object in the current release, the list will grow eventually.
Passing a string value like “Structure” will not produce the result you are looking for.
Nevertheless, this can be achieved via Python today, if you look in the previous posts on the forum you will find something similar for Feature Lines that should give you an idea of how to do it LINK.
I’m working with a couple of colleagues on a Dynamo package to support among other things Pipe Networks workflow to leverage visual programming and expand what you can do with Dynamo for Civil 3D out of the box.
Could you be more specific on what you are trying to accomplish? Maybe I can help.