Plugged EGR at head. What to expect?

Unfortunately that gasket material that blocks off the EGR that comes with the 1250's will disenegrate. An easy way to block off the heat passage is to get an expandable rubber plug. I got one from Pep Boys. It has a bolt running through it that you tighten and a washer on each side. You put it in the center hole on top of your lower intake. (the round hole in the middle of the lower). Then I pluged off the water lines going to the EGR Spacer. It worked for me.
You should not get any check engine lights. You can put a block off plate on the EGR if you want to but you have to leave the EGR plugged in to the harness. It will change you timing and fuel curve if you leave it unplugged.

also, some folks experience detonation...just something to listen for and be aware of. good luck.