Sounds like you gotta plan.
I've got some pics on here somewhere of what I did to the cross member in case you need to look at options to get an idea. I know some guys position them with U-bolts but this doesn't seem safe enough for me because I use mine as a daily driver. Also get the two driveshafts off the 90 so you can mix n match.
Will those seats fit in there okay? Just curious because I need to get some new ones BAD (had a spring pop me in the huevos the other day). I was under the impression that the 3rd gen seats don't fit well in to the 1st gen cab, that they are too big to get aligned well.