i installed my cat and jdm 4-1 header a few weeks ago, and ran into the problem that when the secondary o2 sensor is installed it hits the shiftlinkage. i just landed up putting a bolt in place of the o2. Running the stock jdm ecu anyway so the o2 doesnt matter.

 

This is a very tight squeeze for the O2 sensor. The heat shield needs to be trimmed for the wires. You could try using some smaller diameter bolts in the 3 bolts flange and rotate the cat a trad, either way, to see if you can get the clearance needed.

 

I had to trim my heat shield to make it work.