While pulling my oil pan I noticed something odd in the header for the rear bank. There's a honeycomb looking obstruction and mine looks like something pushed thru in a small spot.

Is this something added to make up for the differences in pipe lengths between the front and rear cyliders and differences in restriction?

And what kinda trouble would I be getting into if I were to seperate the front and rear cylinders and make a dual exhaust?
I figure the O2's will prolly muck everything up, right?