Thank you for your expertise, time and suggestions.
I have seen the WP 3820 generic system you referenced. If only the facing surface helps, I don't know why the 1" gap in the middle is relevant. It would seem the gap could be replaced with anything, or eliminated.
Does pretty much any solution with double 5/8" on the exterior qualify as 2hr, but not much else? I don't understand how U360 rates as 2hr. Can you explain that? See the additional attachment.