Snag while changing heater core

[mexocutioner]

I was going to change the heater core, and this piece of white metal is blocking one of the mounting screws for it. That is not shown in the Bentley manual or on any other threads for dash removal. But, behind that metal piece, there is another black metal bar running up into the main dash.

What is that? Will I mess anything up unbolting the bottom of it to take that white metal piece off to reach the heater core?

[mexocutioner]

okay I went ahead and pulled that white piece out.

New Question: How the hell do you get the top most screw out, where the heater core attaches to the pipes? The pipes don't budge in any direction and theres not even a half inch to get to the screw. The ratchet head won't fit on by itself even!