The trick I learned was a set of swivel sockets from Sears. I used a 17mm swivel socket with another swivel attached and then a 12" and a 6" extension. The combination of swivels made it easy to get all the nuts off within 30 minutes. The uppers have to be removed from above. I heated an old 17mm combination wrench in a vise and bent it with a hammer to about a 15 degree angle. this allowed the wrench to slide on the upper nut on both sides while clearing the firewall. The pipes could not be removed even with the engine removed though so I'm guessing you would have to drop the sub-frame to create enough room for the cats to clear the trans. Good luck if you try this one.

 

Hehe, what exactly are we talking about here?