Say I wanted to publish some material that was formatted as in this example: “Character Name (Stat Block).” How do I keep the Product Identity separate from the Open Game Content?
You could clearly identify the Character Name as Product Identity elsewhere in the work. Assuming that the stat block was derived from other Open Game Content, the stat block must be clearly identified as Open Game Content (it will be Open Game Content even if you don’t clearly identify it, but you have the burden to identify such content when you distribute the work).