Just sealed it a few hours ago, put a copper tube in between it and I managed to get my hand around the main pipe so there's epoxy putty all around it. Now I'm gonna let it sit still for a day to cure since it's been cold here.
I have a concern now about the air flow, the copper tube being in there has reduced it a fair bit, could this cause any issues?
Maybe if it had a very narrow opening, but probably not otherwise. The inlet to the dpfe is usually quite a bit thinner than the pipe itself. The pressure reading that it's getting from the flow in the connected pipe shouldn't change because of the size of the "venturi sampling tube."
I'll keep my fingers crossed for you that you don't wind up with an EGR-related code, let us know how it goes.