Modifying a dual plane??

I picked up an LD4B from Karl for Dads 67 cuda :blob: The plenum has not been modified at all. Im curious as to whether I should modify and if so, how "deep" do I cut it down?
What are the pros/cons of doing this mod?
Dad n I redid the top end, click the link at the bottom for the cam specs. Car has
1405 Eddy carb
904 trans
3:23 sure grip

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=665&sb=2

Thanks
Steve