This is for a quick drop plugin, and I'm getting my references from the panel selection list. Generally, I use a "To more specific class" to get specific class reference type and thus the appropriate methods or property nodes, based on the ClassName. The ClassName I'm getting is "Property".
The problem I was having is that I couldn't find the specific class I needed for the "To more specific class" function. The answer is, Generic->GObject->Node->Growable Function-> Object Function->Property.
From there you get the PropertyItems list via property node and iterate through that, toggling the IsWrite property.