Figured I'd update this thread with the approach that I did. The steering box is in the exact location in relation to the '86 crossmember (basically 2" up and 1" forward.) I had to make some pretty gnarly notches to clear the draglink and idler/pitman arms. I'm not completely done with it. Everything is just tacked for now. I'm going to box the frame and brace the top part of the adapter plate. Anyways, here's the pics in case somebody is looking to go this route when pancaking a crossmember.
There's a few more pics in my build thread if you're interested.