your gonna get a CEL if you run without the cat in the stock manifold - ECM checks for different readings before and after cat.
You might want to look for P28 ECM, convert the harness over and get a header for a 92-95 which locates O2 in front - OBD2 sucks! I wonder if anyone else has fixed this problem with their DX and kept their OBD2 setup to not run into emmisions - smog check issues??