Yes, if you are deleting the EGR you will need a block off plate. I havent yet done it on my 96 GMC sierra but I have done it on my supercharged for lightning. I capped the header and blocked off the other end with a kit. Should be the same for the GMC when I do the headers in a month or so.
Let me know what kit you end up getting and how everything turns out.
Let me know what kit you end up getting and how everything turns out.