22re question

For the Yota gurus, I'm putting together a 93 efi swap (for better or worse), and had a question about something I noticed.  My 84 exhaust post-manifold remains two pipes almost all the way to the cat, but I noticed that the 92 motor that I have (and other late exhausts) combine into one pipe right after the manifold. 

Anyone feel either or style makes a difference?

Which also brings me to my next question, which is that I was operating under the assumption that my O2 sensor would go in the manifold, but it occured to me that it might be right before the cat as well...  Any experience either way with that?

Finally, I would like to get a plug for my fuel pump (since my 84 didn't come with one), is the stealership my only option?

Thanks guys!

If you must run an O2 down by the cat instead of in the manifold then it needs to be a 4-wire heated type.  Which type was stock in 93?