Here's an update:
Cut down the size of the panel braces with a dremel, to make room for the piece holding the rear panel together.
BEFORE
AFTER
On side sanded:
Both sides sanded:
Chopped the rear panel, and will fill it soon(HOW?!).
Believe me, it's an extremely tight fit.
More to come soon! What are my options for filling that gap?
Thanks guys!